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101.
Stuart G. Fisher Nancy B. Grimm Eugènia Martí Robert M. Holmes Jeremy B. Jones Jr. 《Ecosystems》1998,1(1):19-34
Stream ecosystems consist of several subsystems that are spatially distributed concentrically, analogous to the elements
of a simple telescope. Subsystems include the central surface stream, vertically and laterally arrayed saturated sediments
(hyporheic and parafluvial zones), and the most distal element, the riparian zone. These zones are hydrologically connected;
thus water and its dissolved and suspended load move through all of these subsystems as it flows downstream. In any given
subsystem, chemical transformations result in a change in the quantity of materials in transport. Processing length is the length of subsystem required to “process” an amount of substrate equal to advective input. Long processing lengths
reflect low rates of material cycling. Processing length provides the length dimension of each cylindrical element of the
telescope and is specific to subsystem (for example, the surface stream), substrate (for instance, nitrate), and process (denitrification,
for example). Disturbance causes processing length to increase. Processing length decreases during succession following disturbance.
The whole stream-corridor ecosystem consists of several nested cylindrical elements that extend and retract, much as would
a telescope, in response to disturbance regime. This telescoping ecosystem model (TEM) can improve understanding of material
retention in running water systems; that is, their “nutrient filtration” capacity. We hypothesize that disturbance by flooding
alters this capacity in proportion to both intensity of disturbance and to the relative effect of disturbance on each subsystem.
We would expect more distal subsystems (for example, the riparian zone) to show the highest resistance to floods. In contrast,
we predict that postflood recovery of functions such as material processing (that is, resilience) will be highest in central
elements and decrease laterally. Resistance and resilience of subsystems are thus both inversely correlated and spatially
separated. We further hypothesize that cross-linkages between adjacent subsystems will enhance resilience of the system as
a whole. Whole-ecosystem retention, transformation, and transport are thus viewed as a function of subsystem extent, lateral
and vertical linkage, and disturbance regime.
Received 15 April 1997; accepted 1 September 1997. 相似文献
102.
Eveline S. J. M. de Bont Anita E. Niemarkt Rienk Y. J. Tamminga Jan L. L. Kimpen Willem A. Kamps Lou H. M. F. de Leij 《Histochemistry and cell biology》1996,106(6):593-598
Lipopolysaccharide (LPS) can induce monocytes to produce various cytokines such as tumor necrosis factor α (TNFα) and interleukin
1β (IL-1β). In the present study, the kinetics of both intracellular and extracellular accumulation of TNFα and IL-1β in LPS
stimulated mononuclear cell (MNC) cultures has been determined. A three-color-immunofluorescence technique was used to detect
intracellular accumulation of cytokines. Intracellular accumulation of TNFα in monocytes starts shortly after initiation of
the culture; i.e., TNFα is detectable after 1 h, reaching a peak level after 3–4 hours with 50–65% of monocytes staining positive.
In parallel with its increased intracellular presence, TNFα was also found in the culture supernatant. The intracellular accumulation
of IL-1β in monocytes became detectable after 2 h of culture in the presence of LPS. After 4 h, a plateau was reached, with
90% of the monocytes being positive. In parallel, but with a little delay, IL-1β could be detected in the culture supernatant.
TNFα and IL-1β can be produced simultaneously in the same monocytes as was shown by a three-color-immunofluorescence technique.
It is concluded that TNFα and IL-1β are good parameters for the early measurement of monocyte activation and that both the
intracellular accumulation in monocytes and the amount of secreted cytokines can be used for such a purpose. The intracellular
accumulation in monocytes can be measured by the three-color-immunofluorescence technique described.
Accepted: 27 August 1996 相似文献
103.
Abstract: The effect of an inhibitor of N -glycosylation of glycoproteins, tunicamycin, on synthesis of PNS myelin proteins was investigated in vitro by using chopped sciatic nerves or spinal roots of 21-day-old Wistar rats. Tunicamycin when incubated with these nerves in the presence of 3 H-labeled fucose, mannose, or glucosamine inhibited the uptake of radioactivity into myelin proteins including some high-molecular-weight proteins, P0 , 23K protein, and 19K protein by amounts ranging from 42 to 79%. Uptake of 14 Camino acid mixture was inhibited much less by tunicamycin, but a new radioactive protein peak appeared when the protein mixtures had been separated by electrophoresis on polyacrylamide gels in the presence of sodium dodecyl sulfate. This protein ran directly in front of the P0 peak, did not correspond to any bands stained by Fast green, and was not labeled by fucose. This peak appeared in increasing larger proportions with progressive time of incubation of nerves with 3 H amino acids in the presence of tunicamycin. The new protein, which cross-reacts with P0 antiserum, was tentatively identified as a nonglycosylated P0 protein that appears to be almost as well incorporated as P0 into the subcellular fraction containing myelin. At this time it is not possible to determine whether the unglycosylated P0 is actually assembled into a site and configuration like that of P0 . 相似文献
104.
Glyphosate-resistant goosegrass. Identification of a mutation in the target enzyme 5-enolpyruvylshikimate-3-phosphate synthase 总被引:2,自引:0,他引:2
The spontaneous occurrence of resistance to the herbicide glyphosate in weed species has been an extremely infrequent event, despite over 20 years of extensive use. Recently, a glyphosate-resistant biotype of goosegrass (Eleusine indica) was identified in Malaysia exhibiting an LD(50) value approximately 2- to 4-fold greater than the sensitive biotype collected from the same region. A comparison of the inhibition of 5-enolpyruvylshikimate-3-phosphate synthase (EPSPS) activity by glyphosate in extracts prepared from the resistant (R) and sensitive (S) biotypes revealed an approximately 5-fold higher IC(50)(glyphosate) for the (R) biotype. Sequence comparisons of the predicted EPSPS mature protein coding regions from both biotypes revealed four single-nucleotide differences, two of which result in amino acid changes. One of these changes, a proline to serine substitution at position 106 in the (R) biotype, corresponds to a substitution previously identified in a glyphosate-insensitive EPSPS enzyme from Salmonella typhimurium. Kinetic data generated for the recombinant enzymes suggests that the second substitution identified in the (R) EPSPS does not contribute significantly to its reduced glyphosate sensitivity. Escherichia coli aroA- (EPSPS deficient) strains expressing the mature EPSPS enzyme from the (R) biotype exhibited an approximately 3-fold increase in glyphosate tolerance relative to strains expressing the mature EPSPS from the (S) biotype. These results provide the first evidence for an altered EPSPS enzyme as an underlying component of evolved glyphosate resistance in any plant species. 相似文献
105.
Sura Shayna A. Delgadillo Aaron Franco Nancy Gu Kelly Turba Rachel Fong Peggy 《Coral reefs (Online)》2019,38(3):425-429
Coral Reefs - Closely cropped algal turfs are characteristic of healthy coral reefs, but unchecked growth can cause transitions into long sediment-laden turfs, which may be an alternative degraded... 相似文献
106.
An RNA pseudoknot in the 3' end of the arterivirus genome has a critical role in regulating viral RNA synthesis 下载免费PDF全文
In the life cycle of plus-strand RNA viruses, the genome initially serves as the template for both translation of the viral replicase gene and synthesis of minus-strand RNA and is ultimately packaged into progeny virions. These various processes must be properly balanced to ensure efficient viral proliferation. To achieve this, higher-order RNA structures near the termini of a variety of RNA virus genomes are thought to play a key role in regulating the specificity and efficiency of viral RNA synthesis. In this study, we have analyzed the signals for minus-strand RNA synthesis in the prototype of the arterivirus family, equine arteritis virus (EAV). Using site-directed mutagenesis and an EAV reverse genetics system, we have demonstrated that a stem-loop structure near the 3' terminus of the EAV genome is required for RNA synthesis. We have also obtained evidence for an essential pseudoknot interaction between the loop region of this stem-loop structure and an upstream hairpin residing in the gene encoding the nucleocapsid protein. We propose that the formation of this pseudoknot interaction may constitute a molecular switch that could regulate the specificity or timing of viral RNA synthesis. This hypothesis is supported by the fact that phylogenetic analysis predicted the formation of similar pseudoknot interactions near the 3' end of all known arterivirus genomes, suggesting that this interaction has been conserved in evolution. 相似文献
107.
Aloke K. Bera Nancy W. Y. Ho Aftab Khan Miroslav Sedlak 《Journal of industrial microbiology & biotechnology》2011,38(5):617-626
Robust microorganisms are necessary for economical bioethanol production. However, such organisms must be able to effectively
ferment both hexose and pentose sugars present in lignocellulosic hydrolysate to ethanol. Wild type Saccharomyces cerevisiae can rapidly ferment hexose, but cannot ferment pentose sugars. Considerable efforts were made to genetically engineer S. cerevisiae to ferment xylose. Our genetically engineered S cerevisiae yeast, 424A(LNH-ST), expresses NADPH/NADH xylose reductase (XR) that prefer NADPH and NAD+-dependent xylitol dehydrogenase (XD) from Pichia stipitis, and overexpresses endogenous xylulokinase (XK). This strain is able to ferment glucose and xylose, as well as other hexose
sugars, to ethanol. However, the preference for different cofactors by XR and XD might lead to redox imbalance, xylitol excretion,
and thus might reduce ethanol yield and productivity. In the present study, genes responsible for the conversion of xylose
to xylulose with different cofactor specificity (1) XR from N. crassa (NADPH-dependent) and C. parapsilosis (NADH-dependent), and (2) mutant XD from P. stipitis (containing three mutations D207A/I208R/F209S) were overexpressed in wild type yeast. To increase the NADPH pool, the fungal
GAPDH enzyme from Kluyveromyces lactis was overexpressed in the 424A(LNH-ST) strain. Four pentose phosphate pathway (PPP) genes, TKL1, TAL1, RKI1 and RPE1 from S. cerevisiae, were also overexpressed in 424A(LNH-ST). Overexpression of GAPDH lowered xylitol production by more than 40%. However, other
strains carrying different combinations of XR and XD, as well as new strains containing the overexpressed PPP genes, did not
yield any significant improvement in xylose fermentation. 相似文献
108.
109.
Nicholas J. Maness Jonah B. Sacha Shari M. Piaskowski Kimberly L. Weisgrau Eva G. Rakasz Gemma E. May Matthew B. Buechler Andrew D. Walsh Nancy A. Wilson David I. Watkins 《Journal of virology》2009,83(19):10280-10285
Understanding the correlates of immune protection against human immunodeficiency virus and simian immunodeficiency virus (SIV) will require defining the entire cellular immune response against the viruses. Here, we define two novel translation products from the SIV env mRNA that are targeted by the T-cell response in SIV-infected rhesus macaques. The shorter product is a subset of the larger product, which contains both the first exon of the Rev protein and a translated portion of the rev intron. Our data suggest that the translation of viral alternate reading frames may be an important source of T-cell epitopes, including epitopes normally derived from functional proteins.The pathway from viral infection to the cellular immune response is not well understood. Despite the importance of T-cell responses in control of AIDS virus replication (1, 3, 8, 22), the sources of the peptides recognized by virus-specific T cells are still being discovered. AIDS virus-specific CD8+ T lymphocytes (CD8-TL) recognize complexes of major histocompatibility complex (MHC) class I and virus-derived epitopes presented on the surface of infected cells. These epitopes can be derived from exogenous viral proteins in the infecting virion (19, 20) or from de novo synthesis of viral proteins (9, 21). Additional sources of epitopes are also being explored (4, 6).CD8-TL can also recognize epitopes derived from translation of viral alternate reading frames (ARFs). Though CD8-TL specific for ARF-derived epitopes have been detected in human immunodeficiency virus (HIV) (2), they remain a largely unexplored source of epitopes that might elicit potent antiviral cellular immune responses. We recently showed that SIVmac239-infected rhesus macaques that spontaneously controlled viral replication, termed elite controllers, made immunodominant CD8-TL responses against an epitope (RHLAFKCLW, or cRW9) derived from an ARF of the env gene (15). This response selected for viral escape in vivo and suppressed viral replication in an in vitro assay. These findings imply that CD8-TL specific for ARF-derived epitopes might be an important component of the total AIDS virus-specific cellular immune response.Here, we show that the cRW9 epitope is translated as part of two distinct products that differ in size due to start codon usage. The larger and more frequent product contains both the first 23 amino acids of the Rev protein (exon 1) and 50 amino acids translated from the rev intron. The smaller is produced by translation initiation at a start codon within the rev intron and is a subset of the larger product. Finally, we show that these products are degraded after translation from the mature Env-encoding mRNA. 相似文献
110.
Li G Vega R Nelms K Gekakis N Goodnow C McNamara P Wu H Hong NA Glynne R 《PLoS genetics》2007,3(1):e8
Premature truncation alleles in the ALMS1 gene are a frequent cause of human Alstr?m syndrome. Alstr?m syndrome is a rare disorder characterized by early obesity and sensory impairment, symptoms shared with other genetic diseases affecting proteins of the primary cilium. ALMS1 localizes to centrosomes and ciliary basal bodies, but truncation mutations in Alms1/ALMS1 do not preclude formation of cilia. Here, we show that in vitro knockdown of Alms1 in mice causes stunted cilia on kidney epithelial cells and prevents these cells from increasing calcium influx in response to mechanical stimuli. The stunted-cilium phenotype can be rescued with a 5' fragment of the Alms1 cDNA, which resembles disease-associated alleles. In a mouse model of Alstr?m syndrome, Alms1 protein can be stably expressed from the mutant allele and is required for cilia formation in primary cells. Aged mice developed specific loss of cilia from the kidney proximal tubules, which is associated with foci of apoptosis or proliferation. As renal failure is a common cause of mortality in Alstr?m syndrome patients, we conclude that this disease should be considered as a further example of the class of renal ciliopathies: wild-type or mutant alleles of the Alstr?m syndrome gene can support normal kidney ciliogenesis in vitro and in vivo, but mutant alleles are associated with age-dependent loss of kidney primary cilia. 相似文献