全文获取类型
收费全文 | 10410篇 |
免费 | 953篇 |
国内免费 | 12篇 |
专业分类
11375篇 |
出版年
2023年 | 45篇 |
2022年 | 122篇 |
2021年 | 218篇 |
2020年 | 118篇 |
2019年 | 157篇 |
2018年 | 203篇 |
2017年 | 204篇 |
2016年 | 287篇 |
2015年 | 490篇 |
2014年 | 546篇 |
2013年 | 691篇 |
2012年 | 848篇 |
2011年 | 828篇 |
2010年 | 531篇 |
2009年 | 455篇 |
2008年 | 694篇 |
2007年 | 633篇 |
2006年 | 593篇 |
2005年 | 571篇 |
2004年 | 539篇 |
2003年 | 470篇 |
2002年 | 471篇 |
2001年 | 139篇 |
2000年 | 88篇 |
1999年 | 116篇 |
1998年 | 130篇 |
1997年 | 89篇 |
1996年 | 73篇 |
1995年 | 40篇 |
1994年 | 63篇 |
1993年 | 59篇 |
1992年 | 59篇 |
1991年 | 53篇 |
1990年 | 68篇 |
1989年 | 49篇 |
1988年 | 42篇 |
1987年 | 52篇 |
1986年 | 38篇 |
1985年 | 28篇 |
1984年 | 46篇 |
1983年 | 34篇 |
1982年 | 38篇 |
1981年 | 29篇 |
1980年 | 34篇 |
1979年 | 39篇 |
1978年 | 27篇 |
1977年 | 21篇 |
1974年 | 26篇 |
1972年 | 22篇 |
1971年 | 20篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
1.
2.
The natural aversion of rats to ethanol was overcome by subjecting rats to immobilization stress for a two-week period during which increasing concentrations of ethanol were offered in the drinking water. The rats subjected to this regimen consumed 47% of total calories as ethanol, indefinitely, following removal of the stress. Ethanol was consumed at a rate of 17.1 g/kg body weight along with sufficient stock diet to assure adequate nutrition in the absence of ethanol. 相似文献
3.
Vincent Anquetil Caroline Le Sommer Agn��s M��reau Sandra Hamon Hubert Lerivray Serge Hardy 《The Journal of biological chemistry》2009,284(47):32370-32383
Alternative splicing of 3′-terminal exons plays a critical role in gene expression by producing mRNA with distinct 3′-untranslated regions that regulate their fate and their expression. The Xenopus α-tropomyosin pre-mRNA possesses a composite internal/3′-terminal exon (exon 9A9′) that is differentially processed depending on the embryonic tissue. Exon 9A9′ is repressed in non-muscle tissue by the polypyrimidine tract binding protein, whereas it is selected as a 3′-terminal or internal exon in myotomal cells and adult striated muscles, respectively. We report here the identification of an intronic regulatory element, designated the upstream terminal exon enhancer (UTE), that is required for the specific usage of exon 9A9′ as a 3′-terminal exon in the myotome. We demonstrate that polypyrimidine tract binding protein prevents the activity of UTE in non-muscle cells, whereas a subclass of serine/arginine rich (SR) proteins promotes the selection of exon 9A9′ in a UTE-dependent way. Morpholino-targeted blocking of UTE in the embryo strongly reduced the inclusion of exon 9A9′ as a 3′-terminal exon in the endogenous mRNA, demonstrating the function of UTE under physiological circumstances. This strategy allowed us to reveal a splicing pathway that generates a mRNA with no in frame stop codon and whose steady-state level is translation-dependent. This result suggests that a non-stop decay mechanism participates in the strict control of the 3′-end processing of the α-tropomyosin pre-mRNA. 相似文献
4.
Rachael V. Gallagher Lesley Hughes Michelle R. Leishman Peter D. Wilson 《Biological invasions》2010,12(12):4049-4063
Potential interactions between climate change and exotic plant invasions may affect areas of high conservation value, such
as land set aside for the protection of endangered species or ecological communities. We investigated this issue in eastern
Australia using species distribution models for five exotic vines under climate regimes for 2020 and 2050. We examined how
projected changes in the distribution of climatically suitable habitat may coincide with the remaining remnants of an endangered
ecological community—littoral rainforests—in this region. The number of known infestations of each weed in tropical, subtropical
and temperate areas was used to assess the likelihood of further expansion into areas projected to provide suitable habitat
under future conditions. Littoral rainforest reserves were consistently predicted to provide bioclimatically suitable habitat
for the five vines examined under both current and future climate scenarios. We explore the consequences and potential strategies
for managing exotic plant invasions in these protected areas in the coming decades. 相似文献
5.
J.N. Beresford J.A. Gallagher M. Gowen M. Couch J. Poser D.D. Wood R.G.G. Russell 《Biochimica et Biophysica Acta (BBA)/General Subjects》1984,801(1):58-65
Cultural adherent human mononuclear cells produce factor(s) which stimulate the release of calcium from new-born mouse calvaria in organ culture. This stimulation of bone resorption is accompanied by an inhibition of the incorporation of [3H]proline into collagen which is independent of increased prostaglandin production by the bone. When human osteoblast-like cells are treated with conditioned medium from human mononuclear cells, collagen accounts for a decreased proportion of the protein synthesised. This effect on matrix synthesis is not accompanied by an inhibitory action of the monocyte-conditioned medium preparations on net cell proliferation. In human osteoblast-like cell cultures, partially purified human interleukin 1 also inhibits the production of the bone-specific protein osteocalcin in a dose-dependent fashion. These observations are consistent with the hypothesis that products of human monocytes similar to, or identical with, human interleukin 1 may be important regulators of bone metabolism and may contribute to the bone loss seen in diseases such as chronic rheumatoid arthritis. 相似文献
6.
Sandra Danner Christiane Kirchhoff Richard Ivell 《Reproductive biology and endocrinology : RB&E》2009,7(1):67-14
Background
Post-meiotically expressed genes in the testis are essential for the proper progression of spermatogenesis, and yet, aside from the construction of individual transgenic mice using specific promoters to drive reporter plasmids, there are only very limited possibilities for relevant and quantitative analysis of gene promoters. This is due to the special nature of post-meiotic haploid cells, which to date are not represented in any appropriate cell-lines. This article reports the development of novel methodology using isolated and cultured rat seminiferous tubules in a multiwell format, into which promoter-reporter constructs can be introduced by a combination of microinjection and electroporation. 相似文献7.
8.
9.
Ante M. Krstulovi Laura Bertani-Dziedzic Sandra Bautista-Cerqueira Stanley E. Gitlow 《Journal of chromatography. B, Analytical technologies in the biomedical and life sciences》1982,227(2):379-389
We describe a direct analysis for the simultaneous quantitative determination of 4-hydroxy-3-methoxyphenylacetic (homovanillic) acid and other monoamine metabolites in human lumbar cerebrospinal fluid, utilizing reversed-phase high-performance liquid chromatography with amperometric detection. In addition, a rapid isocratic separation was developed for homovanillic acid in the presence of other endogenous compounds.Twenty-five unselected diagnostic specimens of human lumbar cerebrospinal fluid were extracted with ethyl acetate and subsequently analyzed using the described method. Chromatographic peaks were identified on the basis of retention behavior and ratio of responses at several oxidation potentials.Although our quantitative results correlate well with the literature values, the data were not interpreted clinically since samples were obtained from routine, diagnostic testing of patients admitted to the medical or neurologic services at the Mount Sinai Hospital. 相似文献
10.