全文获取类型
收费全文 | 9335篇 |
免费 | 880篇 |
国内免费 | 3篇 |
出版年
2022年 | 61篇 |
2021年 | 131篇 |
2020年 | 65篇 |
2019年 | 73篇 |
2018年 | 114篇 |
2017年 | 107篇 |
2016年 | 195篇 |
2015年 | 334篇 |
2014年 | 340篇 |
2013年 | 519篇 |
2012年 | 548篇 |
2011年 | 509篇 |
2010年 | 368篇 |
2009年 | 295篇 |
2008年 | 473篇 |
2007年 | 506篇 |
2006年 | 441篇 |
2005年 | 437篇 |
2004年 | 426篇 |
2003年 | 436篇 |
2002年 | 424篇 |
2001年 | 148篇 |
2000年 | 116篇 |
1999年 | 128篇 |
1998年 | 157篇 |
1997年 | 97篇 |
1996年 | 91篇 |
1995年 | 107篇 |
1994年 | 66篇 |
1993年 | 79篇 |
1992年 | 93篇 |
1991年 | 103篇 |
1990年 | 110篇 |
1989年 | 93篇 |
1988年 | 80篇 |
1987年 | 84篇 |
1986年 | 81篇 |
1985年 | 80篇 |
1984年 | 98篇 |
1983年 | 65篇 |
1982年 | 87篇 |
1981年 | 95篇 |
1980年 | 69篇 |
1979年 | 61篇 |
1978年 | 80篇 |
1977年 | 57篇 |
1974年 | 73篇 |
1973年 | 72篇 |
1972年 | 57篇 |
1970年 | 58篇 |
排序方式: 共有10000条查询结果,搜索用时 531 毫秒
1.
Margaret Garden 《BMJ (Clinical research ed.)》1983,287(6402):1381
2.
Thorsten Thye Genevieve Scarisbrick Edmund N. L. Browne Margaret Amanua Chinbuah John Gyapong Ivy Osei Ellis Owusu-Dabo Stefan Niemann Sabine Rüsch-Gerdes Christian G. Meyer Rolf D. Horstmann 《PloS one》2009,4(7)
The gene of Cytotoxic T Lymphocyte-associated Antigen 4 (CTLA4), a negative regulator of T lymphocytes, contains a single-nucleotide polymorphism (SNP) at position +6230A->G (ct60A->G), which has been found associated with several autoimmune diseases and appears to reduce T-cell inhibitory activity. In Ghana, West Africa, we compared the frequencies of CTLA4 +6230 A/G and 6 haplotype-tagging SNPs in 2010 smear-positive, HIV-negative patients with pulmonary tuberculosis (TB) and 2346 controls matched for age, gender and ethnicity. We found no difference in allele frequencies between cases and controls. However, +6230A and a distinct CTLA4 haplotype and a diplotype comprising the +6230A allele were significantly less frequent among cases with large opacities in chest radiographs compared to those with small ones (Pcorrected [cor] = 0.002, Pcor = 0.00045, P = 0.0005, respectively). This finding suggests that an increased T-cell activity associated with the CTLA4 +6230G allele contributes to pathology rather than to protection in pulmonary TB. 相似文献
3.
Effects on Plant Growth Produced by Azotobacter paspali Related to Synthesis of Plant Growth Regulating Substances 总被引:2,自引:2,他引:0
S ummary . Treating seedling roots of several plant species with cultures of Azotobacter paspali changed plant growth and development and significantly increased weight of leaves and roots; effects were probably caused by plant growth regulators. Culture supernatant fluids contained indolyl-3-acetic acid, at least 3 gibberellins and 2 cytokinins. The added inoculum of A. paspali survived in plant rhizospheres for only a few weeks and no nitrogen was fixed in the root zone of young Paspalum notatum , the grass with which A. paspali is associated. 相似文献
4.
5.
F. Hofhansl W. Wanek S. Drage W. Huber A. Weissenhofer A. Richter 《Biogeochemistry》2011,106(3):371-396
Bulk precipitation and throughfall were collected in a wet lowland rainforest in SW Costa Rica on an event basis to allow
modelling the contributions of dry deposition and canopy exchange to nutrient inputs and internal cycling of nutrients. Estimates
based on bulk precipitation underestimated total atmospheric deposition to tropical rainforests by up to 10-fold ignoring
the contributions of dry deposition. Canopy exchange contributed most of the aboveground inputs to the forest soil of Na+, about half for K+, 10% for P and Mg2+ and negligible for N, C and other elements. Tree species composition did not account for the differences found in net throughfall
between forest sites, and vegetation structure (plant area index) had only a small effect on net throughfall. Forest regrowth
affected net throughfall through reduced soil fertility and differences in leaf traits. Topography most significantly affected
net throughfall via increased dry deposition at sites of higher elevation and via soil fertility and increased canopy exchange
at down slope sites. 相似文献
6.
H Zitzer H H H?nck D B?chner D Richter H J Kreienkamp 《The Journal of biological chemistry》1999,274(46):32997-33001
By using the yeast two-hybrid system we identified a novel protein from the human brain interacting with the C terminus of somatostatin receptor subtype 2. This protein termed somatostatin receptor interacting protein is characterized by a novel domain structure, consisting of six N-terminal ankyrin repeats followed by SH3 and PDZ domains, several proline-rich regions, and a C-terminal sterile alpha motif. It consists of 2185 amino acid residues encoded by a 9-kilobase pair mRNA; several splice variants have been detected in human and rat cDNA libraries. Sequence comparison suggests that the novel multidomain protein, together with cortactin-binding protein, forms a family of cytoskeletal anchoring proteins. Fractionation of rat brain membranes indicated that somatostatin receptor interacting protein is enriched in the postsynaptic density fraction. The interaction of somatostatin receptor subtype 2 with its interacting protein was verified by overlay assays and coimmunoprecipitation experiments from transfected human embryonic kidney cells. Somatostatin receptor subtype 2 and the interacting protein display a striking overlap of their expression patterns in the rat brain. Interestingly, in the hippocampus the mRNA for somatostatin receptor interacting protein was not confined to the cell bodies but was also observed in the molecular layer, suggesting a dendritic localization of this mRNA. 相似文献
7.
Margaret Jacobi 《BMJ (Clinical research ed.)》1981,283(6304):1444-1445
8.
9.
By combined application of chemical pretreatments, capillary gas-chromatography and mass spectrometry it was possible to enlighten the structure of atypical fatty acids with hydroxy groups and cyclopropane rings under the use of only a few of reference substances. The direct alkaline saponification of the sample with liberation of fatty acids and following methylation with boron trifluoride/methanol or diazomethane was proved to be the best method regarding to precision and speed of the sample cleanup. 相似文献
10.
R Vlasak O Wiborg K Richter S Burgschwaiger J Vuust G Kreil 《European journal of biochemistry》1987,169(1):53-58
From a genomic library of Xenopus laevis, two genes coding for different preprocaeruleins have been isolated and sequenced. These correspond to the type I and type III precursors analyzed previously at the cDNA level [Richter, K., Egger, R. and Kreil, G. (1986) J. Biol. Chem. 261, 3676-3680]. The type III gene comprises eight exons; the type I apparently contains eight exons as well, of which six have been sequenced. The genetic information for the dekapeptide caerulein is present on small exons of 45 base pairs. The two genes are highly homologous in their 5'-flanking region, the exon/intron boundaries, and long stretches of intron sequences. A possible scheme for the evolution of this small family of genes through exon and gene duplications is presented. In the type I gene, in place of one of the caerulein exons, a potential exon with conserved splice sites was discovered. If expressed in some frog cells, this exon would code for a new peptide 60% homologous to caerulein. 相似文献