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101.
102.
Compartmentation and flux characteristics of nitrate in spruce 总被引:8,自引:0,他引:8
The radiotracer13N was used to undertake compartmental analyses for NO
3
–
in intact non-mycorrhizal roots ofPicea glauca (Moench) Voss. seedlings. Three compartments were defined, with half-lives of exchange of 2.5 s, 20 s, and 7 min. These were identified as representing surface adsorption, apparent free space, and cytoplasm, respectively. Influx, efflux, and net flux as well as cytoplasmic and apparent-free-space nitrate concentrations were estimated for three different concentration regimes of external nitrate. After exposure to external NO
3
–
for 3 d, influx was calculated to be 0.09 mol·g–1·h–1 (at 10 M [NO
3
–
]o), 0.5mol·g–1·h–1 (at 100 M [NO
inf3
sup–
]o), and 1.2 mol · g–1· h–1 (at 1.5 mM [NO
3
–
]o). Efflux increased with increasing [NO
3
–
]o, constituting 4% of influx at 10 M, 6% at 100 M, and 21% at 1.5 mM. Cytoplasmic [NO
3
–
] was estimated to be 0.3 mM at 10 uM [NO
3
–
]o, 2mM at 100 M [NO
3
–
]o, and 4mM at 1.5 mM [NO
3
–
]o, while free-space [NO
3
–
] was 16 M, 173 M, and 2.2 mM, respectively. A series of experiments was carried out to confirm the identity of the compartments resolved by efflux analysis. Pretreatment at high temperature or application of 2-chloro-ethanol, sodium dodecyl sulphate or hydrogen peroxide made it possible to distinguish the metabolic (cytoplasmic) phase from the remaining two (physical) phases. Likewise, varying [Pi] of the medium altered efflux and thereby [NO
3
–
]cyt, but did not affect [NO
3
–
]free space.Abbreviations and Symbols [NO
3
–
]cyt
cytoplasmic NO
3
–
concentration
- [NO
3
–
]free space
apparent-free-space NO
3
–
concentration
- [NO
3
–
]o
concentration of NO
3
–
in the external solution
-
NO
3
–
flux
- co
efflux from the cytoplasm
- oc
influx to the cytoplasm
- net
net flux
- xylem
flux to the xylem
- red/vac
combined flux to reduction and the vacuole
The research was supported by a Natural Sciences and Engineering Research Council, Canada, grant to Dr. A.D.M. Glass and by a University of British Columbia Graduate Fellowship to Herbert J. Kronzucker. Our thanks go to Dr. M. Adam and Mr. P. Culbert at the particle accelerator facility TRIUMF on the University of British Columbia Campus for providing13NO
3
–
, Drs. R.D. Guy and S. Silim for providing plant material, and Dr. M.Y. Wang, Mr. J. Mehroke and Mr. P. Poon for assistance in experiments and for helpful discussions. 相似文献
103.
It is widely held that there was a phosphate compound in prebiotic chemistry that played the role of adenosine triphosphate and that the first living organisms had ribose-phosphate in the backbone of their genetic material. However, there are no known efficient prebiotic synthesis of high-energy phosphates or phosphate esters. We review the occurrence of phosphates in Nature, the efficiency of the volcanic synthesis of P4O10, the efficiency of polyphosphate synthesis by heating phosphate minerals under geological conditions, and the use of high-energy organic compounds such as cyanamide or hydrogen cyanide. These are shown to be inefficient processes especially when the hydrolysis of the polyphosphates is taken into account. For example, if a whole atmosphere of methane or carbon monoxide were converted to cyanide which somehow synthesized polyphosphates quantitatively, the polyphosphate concentration in the ocean would still have been insignificant. We also attempted to find more efficient high-energy polymerizing agents by spark discharge syntheses, but without success. There may still be undiscovered robust prebiotic syntheses of polyphosphates, or mechanisms for concentrating them, but we conclude that phosphate esters may not have been constituents of the first genetic material. Phosphoanhydrides are also unlikely as prebiotic energy sources.
Correspondence to: S.L. Miller 相似文献
104.
José A. A. Sant''Ana Pereira Arnold De Haan Andy Wessels Antoon F. M. Moorman Anthony J. Sargeant 《The Histochemical journal》1995,27(9):715-722
Summary In the present study we report a novel histochemical method which, by sequential pre-incubations in alkaline and acidic media,
selectively differentiates muscle fibres expressing myosin heavy chain IIX, on the basis of a specific profile for myofibrillar
actomyosin ATPase (mATPase) activity. The enzyme reactions were tested for specificity by means of anti-myosin heavy chain
monoclonal antibodies, which were characterized on Western blots of muscle homogenates. Enzyme histochemical reactions with
the traditional pH buffers were compared to those of the new method and, in conjunction with the immunoreactions, used to
confirm the relationship between MyHC expression and the distinct profiles for mATPase. Imrnunohistochemical reactions demonstrated
that the new method only differentiates those fibres expressing myosin heavy chain IIX. The method revealed a continuum in
which the intermediate staining intensities corresponded to hybrid fibres expressing myosin heavy chain IIX in combination
with either the IIA or IIB forms. Quantitative histochemistry and immunohistochemistry (by image analysis), used to examine
the relationship between staining intensities for mATPase and amounts of myosin heavy chain IIX expression, revealed that
the new method discriminates well between hybrid fibres expressing variable amounts of the IIX isoform (r2 = 0.93). 相似文献
105.
Nathaniel M. Bachrach Wilmot B. Valhmu Enrico Stazzone Anthony Ratcliffe W. Michael Lai Van C. Mow 《Journal of biomechanics》1995,28(12):1561-1569
Explant loading experiments were conducted to investigate the effect of load duration on proteoglycan synthesis. A compressive load of 0.1 MPa applied for 10 min was found to stimulate proteoglycan synthesis, while the same load applied for 20 h suppressed synthesis. This bimodal response suggests that the cells are responding to different mechanical stimuli as time progresses. A theoretical model has therefore been developed to describe the mechanical environment perceived by cells within soft hydrated tissues (e.g. articular cartilage) while the tissue is being loaded. The cells are modeled, using the biphasic theory, as fluid-solid inclusions embedded in and attached to a biphasic extracellular matrix of distinct material properties. A method of solution is developed which is valid for any axisymmetric loading configuration, provided that the cell radius, a, is small relative to the tissue height, h (i.e. h/a 1). A closed-form analytical solution for this inclusion problem is then presented for the confined compression configuration. Results from this model show that the mechanical environment in and around the cells is time dependent and inhomogeneous, and can be significantly influenced by differences in properties between the cell and the extracellular matrix. 相似文献
106.
The ability of type II DNA topoisomerases to perturb the equilibrium distributions of DNA topoisomers is a consequence of their ability to hydrolyse ATP. A sliding mechanism of topoisomerase action has been proposed to account for this phenomenon. 相似文献
107.
Murine CXCR-4 is a functional coreceptor for T-cell-tropic and dual-tropic strains of human immunodeficiency virus type 1. 总被引:3,自引:2,他引:1 下载免费PDF全文
The human chemokine receptor hCXCR-4 serves as a coreceptor for T-cell-tropic (T-tropic) and dual-tropic strains of human immunodeficiency virus type 1 (HIV-1). We have isolated a homolog of hCXCR-4 from a murine T-cell cDNA library and have examined its ability to function as an HIV-1 coreceptor. mCXCR-4 was found to be 91% identical to the human receptor at the amino acid level, with sequence differences concentrated in extracellular domains. Surprisingly, coexpression of both hCD4 and mCXCR-4 on either simian or murine cell lines rendered them permissive for HIV-1-induced cell fusion, indicating that mCXCR-4 is a functional HIV-1 coreceptor. As with hCXCR-4, coreceptor function was restricted to T-tropic and dual-tropic HIV-1 strains. Ribonuclease protection analysis indicated that mCXCR-4 mRNA was expressed in only two of six murine cell lines tested. In contrast, Northern blot analysis of human and mouse tissues revealed that CXCR-4 is widely expressed in both species in vivo. Overall, these data suggest that the reported lack of susceptibility of hCD4+ murine cells to HIV-1 infection in vitro is, at least in part, due to a lack of mCXCR-4 expression rather than a lack of coreceptor function. 相似文献
108.
Christophe Philippe Ccile Arnould Frdrique Sloan Hans van Bokhoven Saskia D. van der Velde-Visser Michle Chery H. Hilger Ropers Simone Gilgenkrantz Anthony P. Monaco Frans P. M. Cremers 《Genomics》1995,27(3)
In a previous study, we have developed a panel of chromosomal rearrangements for the physical mapping of the q13-q21 region of the human X chromosome (Philippe et al., Genomics 17: 147-152, 1993). Here, we report the physical localization of 36 additional polymorphic markers by polymerase chain reaction analysis. The high density of chromosomal breakpoints in Xq21 allows us to map 58 DNA loci in 22 intervals. As a result, this segment of the X chromosome is saturated with approximately three sequence tagged sites per megabase of DNA, which will facilitate the construction of a YAC contig of this region. 相似文献
109.
David E. Lacy Anthony W. Smith David E. Stableforth Grace Smith Peter H. Weller Michael R.W. Brown 《FEMS immunology and medical microbiology》1995,10(3-4):253-262
Abstract Burkholderia cepacia (Pseudomonas cepacia) is now recognised as an important pathogen in cystic fibrosis patients, and several reports have suggested that sputum-culture-proven colonisation occurs despite the presence of specific antibody. In an attempt to establish the use of antibody studies as diagnostic and prognostic indicators of B. cepacia infection, we have examined the IgG response to B. cepacia outer membrane proteins and lipopolysaccharide in patients also colonised with P. aeruginosa . The B. cepacia strains were grown in a modified iron-depleted chemically defined medium and outer membrane components examined by SDS-PAGE and immunoblotting. IgG antibodies were detected against B. cepacia outer membrane antigens, which were not diminished by extensive preadsorption with P. aeruginosa . The response to B. cepacia O-antigen could be readily removed by adsorption of serum either with B. cepacia whole cells or purified LPS, whereas we were unable to adsorb anti-outer membrane protein antibodies using B. cepacia whole cells. The inability to adsorb anti-outer membrane protein antibodies using B. cepacia whole cells maybe due to non-exposed surface epitopes. Several B. cepacia sputum-culture negative patients colonised with P. aeruginosa had antibodies directed against B. cepacia outer membrane protein. This study suggests that there is a specific anti- B. cepacia LPS IgG response, which is not due to antibodies cross-reactive with P. aeruginosa . Our studies indicate that much of the B. cepacia anti-outer membrane protein response is specific and not attributable to reactivity against co-migrating LPS. 相似文献
110.
J. S. Hill Gaston Lesley E. Wallace Alan B. Rickinson M. Anthony Epstein Donald Pious 《Immunogenetics》1984,19(6):475-486
Mutants of the EB virus-transformed cell line T5-1 (HLA-Al, 2; B8, 27), bearing well-characterized alterations in HLA-A2 antigen expression and unable to bind the HLA-A2-specific monoclonal antibody 13137.2, have been tested for their susceptibility to EB virus-specific cytolysis using effector T-cell preparations functionally restricted through relevant HLA antigens. Initial experiments first confirmed that the parent line T5-1 was susceptible to cytolysis by both common A2-restricted and 1327-restricted effector cells. While those T5-1 mutants with little or no surface A2 expression were not lysed by A2-restricted effectors, those targets with quantitatively normal expression of mutant A2 molecules were as susceptible to A2-restricted lysis as the parent line itself. In contrast, all the T5-1 mutant lines were susceptible to B27-restricted cytolysis. The results demonstrate that experimentally induced mutations of HLA-A2 antigen structure, affecting a serologically defined site on the molecule, can occur without altering that same molecule's expression of the T cell-restricting determinant(s). Such experimentally induced mutations are quite different from the naturally occurring variant A2 antigens which are present within the serologically defined A2 antigen group and which show changes at the T cell-restricting site. 相似文献