全文获取类型
收费全文 | 63803篇 |
免费 | 4995篇 |
国内免费 | 5227篇 |
专业分类
74025篇 |
出版年
2024年 | 173篇 |
2023年 | 877篇 |
2022年 | 2017篇 |
2021年 | 3512篇 |
2020年 | 2296篇 |
2019年 | 2863篇 |
2018年 | 2803篇 |
2017年 | 2001篇 |
2016年 | 2775篇 |
2015年 | 3951篇 |
2014年 | 4709篇 |
2013年 | 5038篇 |
2012年 | 5813篇 |
2011年 | 5217篇 |
2010年 | 3307篇 |
2009年 | 2809篇 |
2008年 | 3290篇 |
2007年 | 2901篇 |
2006年 | 2587篇 |
2005年 | 2183篇 |
2004年 | 1730篇 |
2003年 | 1590篇 |
2002年 | 1314篇 |
2001年 | 1045篇 |
2000年 | 943篇 |
1999年 | 976篇 |
1998年 | 585篇 |
1997年 | 554篇 |
1996年 | 546篇 |
1995年 | 497篇 |
1994年 | 483篇 |
1993年 | 386篇 |
1992年 | 472篇 |
1991年 | 364篇 |
1990年 | 326篇 |
1989年 | 268篇 |
1988年 | 178篇 |
1987年 | 146篇 |
1986年 | 128篇 |
1985年 | 119篇 |
1984年 | 77篇 |
1983年 | 70篇 |
1982年 | 53篇 |
1981年 | 18篇 |
1980年 | 12篇 |
1979年 | 13篇 |
1975年 | 2篇 |
1966年 | 1篇 |
1965年 | 1篇 |
1950年 | 3篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
1.
2.
3.
4.
Bing Xia Haiping Ke Wei Jiang Masayori Inouye 《The Journal of biological chemistry》2002,277(8):6005-6011
The 5'-end region of cspA mRNA contains a Cold Box sequence conserved among several cold-shock mRNAs. This region forms a stable stem-loop structure followed by an AU-rich sequence. Here we show that the Cold Box region is essential for the normal scale of cspA mRNA induction after cold shock because a deletion of the stem-loop significantly destabilizes the mRNA and reduces the cold shock-induced cspA mRNA amount by approximately 50%. The AU-rich track, however, slightly destabilizes the mRNA. The integrity of the stem is essential for the stabilizing function, whereas that of the loop sequence is less important. Overexpression of a mutant cspA mRNA devoid of both the AUG initiation codon and the coding sequence results in a severe growth inhibition at low temperature along with a derepression of the chromosomal cspA expression. Furthermore, the overexpressed RNA is stably associated with the 30 S and 70 S ribosomes. Our results demonstrate that the AUG initiation codon and the coding region containing the downstream box are not required for cspA mRNA to bind ribosomes and that the 5'-untranslated region by itself has a remarkable affinity to ribosomes at low temperature. 相似文献
5.
Transcriptional regulatory network triggered by oxidative signals configures the early response mechanisms of japonica rice to chilling stress 总被引:3,自引:0,他引:3
6.
Inflammatory responses mediated by activated microglia play a pivotal role in the pathogenesis of human immunodeficiency virus type 1 (HIV-1)-associated neurocognitive disorders. Studies on identification of specific targets to control microglia activation and resultant neurotoxic activity are imperative. Increasing evidence indicate that voltage-gated K+ (Kv) channels are involved in the regulation of microglia functionality. In this study, we investigated Kv1.3 channels in the regulation of neurotoxic activity mediated by HIV-1 glycoprotein 120 (gp120)-stimulated rat microglia. Our results showed treatment of microglia with gp120 increased the expression levels of Kv1.3 mRNA and protein. In parallel, whole-cell patch-clamp studies revealed that gp120 enhanced microglia Kv1.3 current, which was blocked by margatoxin, a Kv1.3 blocker. The association of gp120 enhancement of Kv1.3 current with microglia neurotoxicity was demonstrated by experimental results that blocking microglia Kv1.3 attenuated gp120-associated microglia production of neurotoxins and neurotoxicity. Knockdown of Kv1.3 gene by transfection of microglia with Kv1.3-siRNA abrogated gp120-associated microglia neurotoxic activity. Further investigation unraveled an involvement of p38 MAPK in gp120 enhancement of microglia Kv1.3 expression and resultant neurotoxic activity. These results suggest not only a role Kv1.3 may have in gp120-associated microglia neurotoxic activity, but also a potential target for the development of therapeutic strategies. 相似文献
7.
R B Widelitz T X Jiang C W Chen N S Stott H S Jung C M Chuong 《Development (Cambridge, England)》1999,126(12):2577-2587
How do vertebrate epithelial appendages form from the flat epithelia? Following the formation of feather placodes, the previously radially symmetrical primordia become anterior-posterior (A-P) asymmetrical and develop a proximo-distal (P-D) axis. Analysis of the molecular heterogeneity revealed a surprising parallel of molecular profiles in the A-P feather buds and the ventral-dorsal (V-D) Drosophila appendage imaginal discs. The functional significance was tested with an in vitro feather reconstitution model. Wnt-7a expression initiated all over the feather tract epithelium, intensifying as it became restricted first to the primordia domain, then to an accentuated ring pattern within the primordia border, and finally to the posterior bud. In contrast, sonic hedgehog expression was induced later as a dot within the primordia. RCAS was used to overexpress Wnt-7a in reconstituted feather explants derived from stage 29 dorsal skin to further test its function in feather formation. Control skin formed normal elongated, slender buds with A-P orientation, but Wnt-7a overexpression led to plateau-like skin appendages lacking an A-P axis. Feathers in the Wnt-7a overexpressing skin also had inhibited elongation of the P-D axes. This was not due to a lack of cell proliferation, which actually was increased although randomly distributed. While morphogenesis was perturbed, differentiation proceeded as indicated by the formation of barb ridges. Wnt-7a buds have reduced expression of anterior (Tenascin) bud markers. Middle (Notch-1) and posterior bud markers including Delta-1 and Serrate-1 were diffusely expressed. The results showed that ectopic Wnt-7a expression enhanced properties characteristic of the middle and posterior feather buds and suggest that P-D elongation of vertebrate skin appendages requires balanced interactions between the anterior and posterior buds. 相似文献
8.
Qibo Jiang Shuguang Li 《Journal of chromatography. B, Analytical technologies in the biomedical and life sciences》1999,727(1-2)
Gabapentin (GBP) is a new antiepileptic drug approved for clinical treatment of partial seizures in the USA. Serum GBP concentrations in 283 patients were studied using high-performance liquid chromatography with fluorescence detection. The standard curves were linear over a range of 60 ng to 15 μg/ml. The coefficient of variations were 3.4 to 8.8% and 1.4 to 9.8% for intra- and inter-assay studies, respectively. The lower limit of quantitation was 10 ng/ml. Of the 283 patients studied, 72.5% had GBP levels between 2 and 10 μg/ml, 14.8% were below 2 μg/ml and 12.7% above 10 μg/ml. The mean±S.E. of GBP in 283 patients was 5.38±0.23 μg/ml. Peak concentrations of more than 15 μg/ml and trough levels as low as 0.1 μg/ml were not uncommon. The method described was rapid, simple, highly sensitive and reproducible. Other antiepileptic drugs and endogenous compounds did not interfere with the assay. 相似文献
9.
Yihe Lu Bojie Fu Liding Chen Zhiyun Ouyang Jianying Xu 《Biodiversity and Conservation》2006,15(8):2813-2827
Resolving the conflicts between biodiversity conservation and socioeconomic development is a global pursuit for the long-run
prospects of the human species. Based on Wenchuan County, a typical county in southwestern China, a group of 20 indicators
quantifying regional biodiversity and socioeconomic development was established to classify and evaluate the county area spatially.
A fuzzy c-means clustering (FCM) algorithm was used as the classification method. Three indices including BD, DL and DR characterizing
the value of biodiversity, the level and rate of socioeconomic development of the delineated regions were formulated. The
results indicated that Wenchuan County was optimally classified into 4 types of regions (region I to IV). The area percentages
of the regions vary widely from 4.3 to 65.7%. The sequences of the regions on biodiversity, socioeconomic development level,
and socioeconomic development rate were, respectively, IV > II > III > I, I > III > II > IV and III >I >II >IV. The spatial
strategy on coordinating biodiversity conservation and regional development is to develop mainly from the east(I, II, III)
and to conserve mainly in the west(IV). Eco-industry, such as eco-tourism and eco-agriculture, need to be emphasized in the
process of regional development. The quantitative methods used here may have a wide applicability. 相似文献
10.