全文获取类型
收费全文 | 4192篇 |
免费 | 341篇 |
国内免费 | 10篇 |
出版年
2024年 | 6篇 |
2023年 | 12篇 |
2022年 | 61篇 |
2021年 | 82篇 |
2020年 | 63篇 |
2019年 | 85篇 |
2018年 | 104篇 |
2017年 | 79篇 |
2016年 | 150篇 |
2015年 | 259篇 |
2014年 | 256篇 |
2013年 | 275篇 |
2012年 | 380篇 |
2011年 | 312篇 |
2010年 | 189篇 |
2009年 | 179篇 |
2008年 | 277篇 |
2007年 | 242篇 |
2006年 | 217篇 |
2005年 | 190篇 |
2004年 | 190篇 |
2003年 | 150篇 |
2002年 | 145篇 |
2001年 | 77篇 |
2000年 | 60篇 |
1999年 | 62篇 |
1998年 | 37篇 |
1997年 | 27篇 |
1996年 | 12篇 |
1995年 | 11篇 |
1994年 | 16篇 |
1993年 | 12篇 |
1992年 | 26篇 |
1991年 | 28篇 |
1990年 | 16篇 |
1989年 | 26篇 |
1988年 | 24篇 |
1987年 | 23篇 |
1986年 | 22篇 |
1985年 | 16篇 |
1984年 | 15篇 |
1983年 | 9篇 |
1982年 | 12篇 |
1981年 | 12篇 |
1980年 | 10篇 |
1979年 | 12篇 |
1977年 | 8篇 |
1975年 | 13篇 |
1974年 | 10篇 |
1973年 | 8篇 |
排序方式: 共有4543条查询结果,搜索用时 31 毫秒
901.
QTL analysis of leaf morphology in tetraploid Gossypium (cotton) 总被引:13,自引:0,他引:13
C. Jiang R. J. Wright S. S. Woo T. A. DelMonte A. H. Paterson 《TAG. Theoretical and applied genetics. Theoretische und angewandte Genetik》2000,100(3-4):409-418
Molecular markers were used to map and characterize quantitative trait loci (QTLs) determining cotton leaf morphology and
other traits, in 180 F2 plants from an interspecific cross between a Gossypium hirsutum genotype carrying four morphological mutants, and a wild-type Gossypium barbadense. The prominent effects of a single region of chromosome 15, presumably the classical ”Okra-leaf” locus, were modified by
QTLs on several other chromosomes affecting leaf size and shape. For most traits, each parent contained some alleles with
positive effects and others with negative effects, suggesting a large potential for adapting leaf size and shape to the needs
of particular production regimes. Twenty one QTLs/loci were found for the morphological traits at LOD≥3.0 and P≤0.001, among which 14 (63.6%) mapped to D-subgenome chromosomes. Forty one more possible QTLs/loci were suggested with 2.0≤LOD<3.0
and 0.001<P≤0.01. Among all of the 62 possible QTLs (found at LOD≥2.0 and P≤0.01) for the 14 morphological traits in this study, 38 (61.3%) mapped to D-subgenome chromosomes. This reinforces the findings
of several other studies in suggesting that the D-subgenome of tetraploid cotton has been subject to a relatively greater
rate of evolution than the A-subgenome, subsequent to polyploid formation.
Received: 26 April 1999 / Accepted: 30 July 1999 相似文献
902.
903.
Jeong BY Jeong WG Moon SK Ohshima T 《Comparative biochemistry and physiology. Part B, Biochemistry & molecular biology》2002,131(2):251-259
The effect of dietary lipid on the fatty acid composition of muscle, testis and ovary of cultured sweet smelt, Plecoglossus altivelis, was investigated and compared with that of wild sweet smelt. Cultured fish were fed three different diets for 12 weeks: a control diet rich in docosahexaenoic acid (DHA, 22:6n-3) and eicosapentaenoic acid (EPA, 20:5n-3) (CO group); a diet deficient in DHA and EPA (DP group); and a diet rich in alpha-linolenic acid (ALA, 18:3n-3), but deficient in DHA and EPA (LP group). The fatty acid composition of muscle and gonad lipids was related with dietary fatty acids. Despite the difference in DHA and EPA content in the diets, muscles and gonads, respectively, contained almost equal levels of DHA and EPA in each CO and DP group. However, the muscle and gonad of the LP group showed a lower level of DHA than other groups, due to having the highest level of ALA. In the wild fish muscle, the DHA content was similar to that of CO and DP groups, but the EPA content showed the highest level in all groups. There was no difference in the muscle fatty acid proportions between male and female. On the other hand, the testes of cultured and wild fish were rich in DHA, EPA, docosapentaenoic acid and arachidonic acid, while ovaries were rich in oleic, palmitoleic, linoleic acids and ALA. Moreover, of all the groups, the fish fatty acid composition of the LP group was closest to that of wild fish. These results indicate that in the sweet smelt, tissue n-3 polyunsaturated fatty acids (PUFAs) greater than C20 can be synthesized from dietary precursors and special fatty acids are preferentially accumulated to the testis or ovary, respectively, to play different physiological functions. 相似文献
904.
The silencing of specific oncogenes via RNA interference (RNAi) holds great promise for the future of cancer therapy. RNAi
is commonly carried out using small interfering RNA (siRNA) composed of a 19 bp duplex region with a 2-nucleotide overhang
at each 3′ end. This classical siRNA structure, however, can trigger non-specific effects, which has hampered the development
of specific and safe RNAi therapeutics. Previously, we developed a novel siRNA structure, called asymmetric shorter-duplex
siRNA (asiRNA), which did not cause the non-specific effects triggered by conventional siRNA, such as off-target gene silencing
mediated by the sense strand. In this study, we first screened potent asiRNA molecules targeting the human c-MET gene, a promising
anticancer target. Next, the activity of a selected asiRNA was further optimized by introducing a locked nucleic acid (LNA)
to maximize the gene silencing potency. The optimized asiRNA targeted to c-MET may have potential as a specific and safe anticancer
RNAi therapeutic. 相似文献
905.
Nam Jin Noh Yowhan Son Jin Woo Koo Kyung Won Seo Rae Hyun Kim Yoon Young Lee Kyung Seun Yoo 《Journal of Plant Biology》2010,53(1):61-69
The nitrogenase activity, root nodule biomass, and rates of nitrogen (N) fixation were measured in 25-year-old pure north-
and south-facing Robinia pseudoacacia stands in an urban forest of Seoul (Kkachisan Mountain) in central Korea. The nitrogenase activity was estimated using an
acetylene reduction (AR) assay, which showed an increasing trend during the early growing season, with sustained high rates
from June through to September with a decrease thereafter. July had the highest nitrogenase activity rate (micromoles C2H4 per gram dry nodule per hour), averaging 95.8 and 115.1 for the north- and south-facing stands, respectively. The maximum
root nodule biomass (kilograms per hectare) was 45.7 and 9.1 for the north- and south-facing stands in July, respectively.
The AR rate appeared to be strongly correlated to the soil temperature (r
2 = 0.68, P < 0.001) and soil pH (r
2 = 0.59, P < 0.001) while root nodule biomass was correlated to the soil temperature (r
2 = 0.36, P < 0.01) and water content (r
2 = 0.35, P < 0.05). The soil temperature showed clear differences between seasons, while there was a significant difference in soil pH,
organic matter, total N concentrations, and available phosphorus between the north- and south-facing stands. The N2 fixation rates during the growing season varied from 0.1 to 37.5 kg N ha−1 month−1 depending on the sampling location and time. The annual N2 fixation rate (kg N per hectare per year) was 112.3 and 23.2 for the north- and south-facing stands, respectively. The differences
in N2 fixation rate between the two stands were due mainly to the differences in total nodule biomass. 相似文献
906.
907.
908.
Bing Shen Ching-On Wong On-Chai Lau Theodosia Woo Suwen Bai Yu Huang Xiaoqiang Yao 《PloS one》2015,10(4)
Mechanical forces exerted on cells impose stress on the plasma membrane. Cells sense this stress and elicit a mechanoelectric transduction cascade that initiates compensatory mechanisms. Mechanosensitive ion channels in the plasma membrane are responsible for transducing the mechanical signals to electrical signals. However, the mechanisms underlying channel activation in response to mechanical stress remain incompletely understood. Transient Receptor Potential (TRP) channels serve essential functions in several sensory modalities. These channels can also participate in mechanotransduction by either being autonomously sensitive to mechanical perturbation or by coupling to other mechanosensory components of the cell. Here, we investigated the response of a TRP family member, TRPC5, to mechanical stress. Hypoosmolarity triggers Ca2+ influx and cationic conductance through TRPC5. Importantly, for the first time we were able to record the stretch-activated TRPC5 current at single-channel level. The activation threshold for TRPC5 was found to be 240 mOsm for hypoosmotic stress and between −20 and −40 mmHg for pressure applied to membrane patch. In addition, we found that disruption of actin filaments suppresses TRPC5 response to hypoosmotic stress and patch pipette pressure, but does not prevent the activation of TRPC5 by stretch-independent mechanisms, indicating that actin cytoskeleton is an essential transduction component that confers mechanosensitivity to TRPC5. In summary, our findings establish that TRPC5 can be activated at the single-channel level when mechanical stress on the cell reaches a certain threshold. 相似文献
909.
While there is literature on excess winter mortality, there are few studies examining the evolution of its trend which may be changing in parallel with global warming. This study aimed to examine the trend in the excess mortality in winter as compared to summer among the older population in a sub-tropical city and to explore its association with extreme weather. We used a retrospective study based on the registered deaths among the older population in Hong Kong during 1976-2010. An Excess Mortality for Winter versus Summer (EMWS) Index was used to quantify the excess number of deaths in winter compared to summer. Multiple linear regressions were used to analyze the trends and its association with extreme weather. Overall, the EMWS Index for ischemic heart disease, cerebrovascular diseases, chronic lower respiratory diseases, pneumonia, and other causes were 43.0%, 34.2%, 42.7%, 23.4% and 17.6%, respectively. Significant decline was observed in the EMWS Index for chronic lower respiratory diseases and other causes. The trend in the index for cerebrovascular diseases depended on the age group, with older groups showing a decline but younger groups not showing any trend. Meteorological variables, in terms of extreme weather, were associated with the trends in the EMWS Index. We concluded that shrinking excess winter mortality from cerebrovascular diseases and chronic lower respiratory diseases was found in a sub-tropical city. These trends were associated with extreme weather, which coincided with global warming. 相似文献