全文获取类型
收费全文 | 50402篇 |
免费 | 4590篇 |
国内免费 | 30篇 |
专业分类
55022篇 |
出版年
2022年 | 363篇 |
2021年 | 766篇 |
2020年 | 456篇 |
2019年 | 574篇 |
2018年 | 709篇 |
2017年 | 653篇 |
2016年 | 1049篇 |
2015年 | 1763篇 |
2014年 | 1955篇 |
2013年 | 2567篇 |
2012年 | 3232篇 |
2011年 | 3304篇 |
2010年 | 2138篇 |
2009年 | 1920篇 |
2008年 | 2741篇 |
2007年 | 2834篇 |
2006年 | 2759篇 |
2005年 | 2639篇 |
2004年 | 2542篇 |
2003年 | 2422篇 |
2002年 | 2309篇 |
2001年 | 558篇 |
2000年 | 458篇 |
1999年 | 617篇 |
1998年 | 736篇 |
1997年 | 552篇 |
1996年 | 475篇 |
1995年 | 429篇 |
1994年 | 419篇 |
1993年 | 445篇 |
1992年 | 483篇 |
1991年 | 420篇 |
1990年 | 409篇 |
1989年 | 397篇 |
1988年 | 367篇 |
1987年 | 329篇 |
1986年 | 357篇 |
1985年 | 376篇 |
1984年 | 456篇 |
1983年 | 374篇 |
1982年 | 479篇 |
1981年 | 494篇 |
1980年 | 391篇 |
1979年 | 322篇 |
1978年 | 335篇 |
1977年 | 295篇 |
1976年 | 330篇 |
1975年 | 225篇 |
1974年 | 280篇 |
1973年 | 272篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
992.
Incubation of human T cells for 18 hr with prostaglandin E2 (PGE2 3 × 10?6M) causes a slight but significant increase in the percentage of Tγ cells and a reduction in Tμ cells. When PGE was added to “non-Tγ” cells, the increase in the percentage of Tγ cells was more marked (from 1.5% Tγ without PGE to 11% Tγ with PGE2, P < 0.001). Supernates from cultures of human monocytes also caused an increase in Tγ cells (10% Tγ without supernate to 18% with supernate, P < 0.01), and this increase was blocked if the monocytes were cultured with indomethacin, a prostaglandin synthetase inhibitor (9% Tγ cells). Thus, monocytes may regulate Fcγ receptors on T cells via PGE2 production. 相似文献
993.
994.
Summary Two mutants of Pachysolen tannophilus were isolated which produced considerably more acetic acid from several sugars than a wild type strain. Such mutants are of potential interest for the production of acetic acid rather than ethanol from lignocellulosic hydrolysates.Issued as NRCC No. 20810. 相似文献
995.
James W. Putney Jr. 《Cell calcium》1983,4(5-6)
In the rat parotid salivary gland, fluid secretion is regulated by alterations in fluxes of monovalent ions.
, stimulation of muscarinic, α-adrenergic or substance P receptors provokes a biphasic increase in membrane permeability to K+ which can be conveniently assayed as efflux of 86Rb. The increased 86Rb flux is thought to arise in response to a receptor mediated elevation in [Ca2+]i which activates Ca2+-activated K+-channels. The biphasic nature of the response is presumably due to a biphasic mode of Ca2+ mobilization by secretagogues; a transient response reflects release of a finite pool of Ca from an intracellular store while a more sustained phase results from Ca entry through receptor operated Ca channels or gates. Calcium also mediates an increased Na+ entry which in turn activates the Na+, K+-pump. The mechanism involved in the regulation of monovalent ion channels by Ca2+ is not understood. 相似文献
996.
Primary cultures of bovine adrenal medullary chromaffin cells were used to examine the effect of replacing divalent cations in the extracellular media on secretion. When calcium was replaced by manganese, nicotine-stimulated secretion was delayed in onset for 3 to 5 minutes, but continued for approximately 60 minutes. In contrast, calcium-supported secretion began immediately on stimulation and plateaued by 10 minutes. 54Mn2+ uptake occurred on stimulation but at a lower rate than 45Ca2+ uptake. There was no delay of 54Mn2+ uptake upon stimulation and 54Mn2+ uptake was considerably prolonged compared to 45Ca2+ uptake. Replacement of calcium with strontium gave results similar to those with calcium, and, in addition, strontium was able to bring about secretion by itself in a manner similar to barium. Inhibition experiments showed that the potency for inhibiting calcium uptake was Cd2+>Mn2+>Ca2+>Sr2+. 相似文献
997.
998.
999.
A low relief, green turf-forming alga of a heterotrichous habit was discovered in the coral reef microcosm, Museum of Natural History, Smithsonian Institution. Erect filaments bore lateral, specialized sporangia and together with basal filaments possessed septal plugs between adjacent cells, grossly similar to the “pit connections” of red algae. Data are presented which: 1) establish the identity of our plant with a plant recently described as Pilinia earleae Gallagher et Humm from the Florida Gulf coast; 2) support our establishment of the new genus Smithsoniella and our transfer of P. earleae to this new taxon. Additional data on pigmentation and cytology are related to the fine structure of other selected green algae to develop and test three hypotheses, viz. Smithsoniella earleae represents either: 1) a symbiotic association between a green and a red alga; 2) an alga which belongs to either the Ulotrichales, Chaetophorales or the Chroolepidales; or 3) an alga representing an evolutionary link between filamentous forms of the Ulvophyceae and members of the coenocytic siphonalean complex (e.g., Codiales or Caulerpales) of the Chlorophyta. Data refute hypotheses 1 and 2 but do lend support to the third hypothesis. 相似文献
1000.
Anterior segment mesenchymal dysgenesis: Probable linkage to the MNS blood group on chromosome 4 总被引:2,自引:1,他引:1
下载免费PDF全文
![点击此处可从《American journal of human genetics》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Robert E. Ferrell Helen M. Hittner Frank L. Kretzer James H. Antoszyk 《American journal of human genetics》1982,34(2):245-249
Thirty-seven blood samples were analyzed for linkage from members of a single family with an anterior segment mesenchymal dysgenesis (ASMD1) with variable expressivity affecting members of at least six generations. Maximum-likelihood analysis for linkage between ASMD1 and 14 biochemical and serological markers in the family showed a probable linkage between ASMD1 and the MNS blood group on the long arm of chromosome 4 (Z = 2.36 at a recombination fraction of .09). 相似文献