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991.
The Lake Taihu drainage basin is an economically developed area with some of the highest population densities in China. The
lake has deteriorated due to ecological destruction and eutrophication. Three short sediment cores from eastern, northeastern
and southwestern Lake Taihu were collected. Total organic carbon (TOC), total nitrogen (TN), pigments, elements and particle
size were analyzed for the purpose of understanding past trophic status and pollution levels. Sedimentation rates were based
on 137Cs or 210Pb methods. Results indicated that sediment particle size became coarser since the 1920s, and the lake was contaminated by
heavy metals, such as Cu and Zn, since the 1970s. A remarkable increase in eutrophication since the 1980s due to increased
loading of untreated effluents from industry, agriculture and urbanization is reflected by total organic carbon, total nitrogen
and pigments in the studied cores. However the onset times of eutrophication in different parts of Lake Taihu were not synchronous. 相似文献
992.
The biophysical characteristics and the pore formation dynamics of synthetic or naturally occurring peptides forming membrane-spanning
channels were investigated by using isolated photoreceptor rod outer segments (OS) recorded in whole-cell configuration. Once
blocking the two OS endogenous conductances (the cGMP channels by light and the Na+:Ca2+,K+ exchanger by removing one of the transported ion species from both sides of the membrane, i.e. K+, Na+ or Ca2+), the OS membrane resistance (R
m
) was typically larger than 1 GΩ in the presence of 1 mM external Ca2+. Therefore, any exogenous current could be studied down to the single channel level. The peptides were applied to (and removed
from) the extracellular OS side in ∼50 ms with a computer-controlled microperfusion system, in which every perfusion parameter,
as the rate of solution flow, the temporal sequence of solution changes or the number of automatic, self-washing cycles were
controlled by a user-friendly interface. This technique was then used to determine the biophysical properties and the pore
formation dynamics of antibiotic peptaibols, as the native alamethicin mixture, the synthesized major component of the neutral
fraction (F50/5) of alamethicin, and the synthetic trichogin GA IV. 相似文献
993.
994.
4-(Methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) is a carcinogenic compound of cigarette smoke that generates electrophilic
intermediates capable of damaging DNA. Recently, we have shown that NNK can modulate mediator production by alveolar macrophages
(AM) and bronchial and alveolar epithelial cells, suggesting that cigarette smoke can alter lung immune response. Thus, we
investigated the effect of NNK and cigarette smoke extract (CSE) on AM capacity to eliminate tumoral cells. Rat AM cell line,
NR8383, was treated with NNK (500 μM) or CSE (3%) and stimulated with lipopolysaccharide (10 ng/ml). The release of cytotoxic
mediators, tumor necrosis factor (TNF) and reactive oxygen species (ROS), was measured in cell-free supernatants using ELISA
and superoxide anion production. TNF- and ROS-dependent cytotoxicity were studied using a 51Chromium-release assay and WEHI-164 and P-815 cell lines. Treatment of AM with NNK and CSE for 18 h significantly inhibited
AM TNF release. CSE exposure resulted in a significant increase of ROS production, whereas NNK did not. TNF-dependent cytotoxic
activity of NR8383 and freshly isolated rat AM was significantly inhibited after treatment with NNK and CSE. Interestingly,
although ROS production was stimulated by CSE and not affected by NNK, CSE inhibited AM ROS-dependent cytotoxicity. These
results suggest that NNK may be one of the cigarette smoke components responsible for the reduction of pulmonary cytotoxicity.
Thus, NNK may have a double pro-carcinogenic effect by contributing to DNA adduct formation and inhibiting AM cytotoxicity
against tumoral cells. 相似文献
995.
Two recent studies on territory occupancy rates of goshawk Accipiter gentilis and gyrfalcon Falco rusticolus report a 2–3-year-delayed numerical response to grouse numbers, which is a requirement for a hypothesis of predator-generated
grouse cycles. The time lags were assumed to reflect the average age of sexual maturity in the raptor species. In southern
Norway, however, subadult (two-year-old) goshawk hens occupied only 18–25% of territories where occupancy was not recorded
in the preceding year, and there was no significant relationship between the proportion of subadults among recruits and grouse
indices two years earlier. We argue that territory occupancy rates are not appropriate indices of total raptor population
levels, but rather reflect the proportion of territorial pairs that attempt to nest. Because this depends on the body condition
of the hens, fluctuations in other important winter resident prey species (most important for the goshawk) and winter weather
(most important for the gyrfalcon) should also be addressed. During 1988–2006, the annual proportion of goshawk territories
with recorded nesting attempts in southern Norway was most closely related to the preceding autumn’s population indices of
black grouse Tetrao tetrix and mountain hare Lepus timidus, whereas the annual proportion of gyrfalcon territories with observations of falcons or with confirmed breeding attempts
in central Norway were best explained by population indices of willow grouse Lagopus lagopus and ptarmigan L. mutus from the previous autumn, and by December temperatures. Hence, our studies do not support the predation hypothesis for grouse
cycles. 相似文献
996.
Growth and reproduction were studied in the laboratory in a cross-designed experimental set-up in four Daphnia galeata subpopulations collected from different locations (with respect to water characteristics) in a reservoir (epilimnion, metalimnion
and hypolimnion in the deepest part of the reservoir near the dam and epilimnion of the upstream part of the reservoir) and
in a laboratory clone of the same species. The results of two-way ANOVA revealed significant effects of the two parameters
manipulated – source of water used for cultures and Daphnia subpopulation – on the life history characteristics of growth and reproduction. The water from the upstream part of the reservoir
was the most favourable culture medium for all characteristics of the Daphnia groups studied (the largest primiparae, clutches and eggs, the shortest postembryonic development time and filtering setae).
The poorest performances were recorded in the downstream, epilimnetic and metalimnetic waters. The primiparae in the hypolimnetic
water were smaller but had relatively larger clutches of smaller eggs and slightly longer postembryonic development times.
The Daphnia subpopulation originating from the hypolimnion had the smallest primiparae, the largest clutches, the smallest eggs and the
shortest postembryonic development, whereas the opposite was found in animals from the epilmnion. These differences in ecologically
relevant traits were supported by analysis of the quasi-neutral genetic markers that indicated significant site-dependent
differences in clonal structure between the subpopulations. There was no consistent trend to higher within-group variance
in the life history traits in the genetically heterogeneous subpopulations from the reservoir compared to the laboratory clone. 相似文献
997.
Traditional cultivation-based methods to quantify microbial abundance are not suitable for analyses of microbial communities
in environmental or medical samples, which consist mainly of uncultured microorganisms. Recently, different cultivation-independent
quantification approaches have been developed to overcome this problem. Some of these techniques use specific fluorescence
markers, for example ribosomal ribonucleic acid targeted oligonucleotide probes, to label the respective target organisms.
Subsequently, the detected cells are visualized by fluorescence microscopy and are quantified by direct visual cell counting
or by digital image analysis. This article provides an overview of these methods and some of their applications with emphasis
on (semi-)automated image analysis solutions. 相似文献
998.
Blombach B Schreiner ME Moch M Oldiges M Eikmanns BJ 《Applied microbiology and biotechnology》2007,76(3):615-623
Intracellular precursor supply is a critical factor for amino acid productivity of Corynebacterium glutamicum. To test for the effect of improved pyruvate availability on l-lysine production, we deleted the aceE gene encoding the E1p enzyme of the pyruvate dehydrogenase complex (PDHC) in the l-lysine-producer C. glutamicum DM1729 and characterised the resulting strain DM1729-BB1 for growth and l-lysine production. Compared to the host strain, C. glutamicum DM1729-BB1 showed no PDHC activity, was acetate auxotrophic and, after complete consumption of the available carbon sources
glucose and acetate, showed a more than 50% lower substrate-specific biomass yield (0.14 vs 0.33 mol C/mol C), an about fourfold
higher biomass-specific l-lysine yield (5.27 vs 1.23 mmol/g cell dry weight) and a more than 40% higher substrate-specific l-lysine yield (0.13 vs 0.09 mol C/mol C). Overexpression of the pyruvate carboxylase or diaminopimelate dehydrogenase genes
in C. glutamicum DM1729-BB1 resulted in a further increase in the biomass-specific l-lysine yield by 6 and 56%, respectively. In addition to l-lysine, significant amounts of pyruvate, l-alanine and l-valine were produced by C. glutamicum DM1729-BB1 and its derivatives, suggesting a surplus of precursor availability and a further potential to improve l-lysine production by engineering the l-lysine biosynthetic pathway.
This study is dedicated to Prof. Dr. Hermann Sahm on the occasion of his 65th birthday. 相似文献
999.
Jonathan T. Hovius Beatrix E. Beisner Kevin S. McCann Norman D. Yan 《Biological invasions》2007,9(3):233-243
As a recent invader of North American lakes, Bythotrephes longimanus has induced large changes in crustacean zooplankton communities through direct predation effects. Here we demonstrate that
Bythotrephes can also have indirect food web effects, specifically on rotifer fauna. In historical time series data, the densities of
the colonial rotifer Conochilus unicornis significantly increased after Bythotrephes invasion in Harp Lake, Ontario. No such changes were observed in a non-invaded reference lake, the nearby Red Chalk Lake.
Evidence for two mechanisms explaining the Conochilus increase was examined based on changes to the crustacean zooplankton community over time. Rapid and severe declines in several
herbivorous species of cladoceran zooplankton after Bythotrephes detection indicated a decrease in exploitative competition pressure on Conochilus. Secondly, a later and significant decline to virtual extinction of native invertebrate predators (Mesocyclops and Leptodora) could account for the observed Conochilus increase which also began 1–2 years after invasion by Bythotrephes. Ultimately, it appears that both reduced competition followed by a loss of native invertebrate predators were necessary
to lead to the large Conochilus densities observed following invader establishment. From this analysis of long-term community data, it appears that Bythotrephes has important indirect, as well as direct, food web effects in newly invaded North American lakes with implications for trophic
relationships. 相似文献
1000.
A trypsin inhibitor was isolated from Cassia obtusifolia by ammonium sulfate precipitation, Sepharose 4B-trypsin affinity and Sephadex G-75 chromatography. The inhibitor consisted
of a single polypeptide chain with a molecular mass of 19, 812.55 Da. It was stable from pH 2 to 12 for 24 h, whereas it was
unstable either above 70°C for 10 min or under reduced conditions. The inhibitor, which inhibited trypsin activity with an
apparent Ki of 0.3 μM, had one reactive site involving a lysine residue. The native inhibitor was resistant to pepsin digestion, whereas
the heated inhibitor produced 40% degree of susceptibility. The disulfide linkage and lysine residue were important in maintaining
its conformation. Partial amino acid sequence of the purified protein showed a high degree of homology with various members
of the Kunitz inhibitor family. Moreover, the inhibitor showed significant inhibitory activity against trypsin-like proteases
present in the larval midgut on Pieris rapae and could suppress the growth of larvae. 相似文献