全文获取类型
收费全文 | 4755篇 |
免费 | 285篇 |
国内免费 | 35篇 |
专业分类
5075篇 |
出版年
2023年 | 14篇 |
2022年 | 41篇 |
2021年 | 59篇 |
2020年 | 33篇 |
2019年 | 38篇 |
2018年 | 51篇 |
2017年 | 63篇 |
2016年 | 90篇 |
2015年 | 145篇 |
2014年 | 180篇 |
2013年 | 332篇 |
2012年 | 308篇 |
2011年 | 287篇 |
2010年 | 174篇 |
2009年 | 172篇 |
2008年 | 295篇 |
2007年 | 310篇 |
2006年 | 294篇 |
2005年 | 280篇 |
2004年 | 279篇 |
2003年 | 280篇 |
2002年 | 263篇 |
2001年 | 82篇 |
2000年 | 79篇 |
1999年 | 74篇 |
1998年 | 56篇 |
1997年 | 64篇 |
1996年 | 32篇 |
1995年 | 37篇 |
1994年 | 33篇 |
1993年 | 34篇 |
1992年 | 41篇 |
1991年 | 54篇 |
1990年 | 64篇 |
1989年 | 48篇 |
1988年 | 49篇 |
1987年 | 33篇 |
1986年 | 41篇 |
1985年 | 30篇 |
1984年 | 21篇 |
1983年 | 23篇 |
1982年 | 22篇 |
1981年 | 19篇 |
1980年 | 16篇 |
1979年 | 13篇 |
1978年 | 12篇 |
1970年 | 13篇 |
1969年 | 12篇 |
1968年 | 14篇 |
1967年 | 10篇 |
排序方式: 共有5075条查询结果,搜索用时 0 毫秒
91.
92.
In order to examine the hypothesis that the thyroidal responsiveness to TSH is under the influence of thyroid hormone, following the T3 injection to the mice, serum T3 concentrations and the response of thyroid tissue to a fixed dose of TSH in terms of intracellular colloid droplet formation was studied. The colloid droplets induced by TSH was significantly reduced when serum T3 was decreasing, while it was significantly increased when serum T3 was increasing. This results demonstrate for the first time the existence of short feed-back loop regulating intra-thyroidal function by circulating T3. To delineate the possible mechanism of action of T3, the thyroid gland of mouse whose serum T3 concentration was elevated by injecting 50 mug T3, was incubated with TSH in vitro. TSH-induced cyclic AMP generation was not inhibited at all but colloid droplet formation was significantly inhibited in the thyroid tissue of the animal whose serum T3 concentration was enormously high. Thus, it was demonstrated that the site at which T3 affects is beyond cylcic AMP generation but prior to endocytosis, being consistent with our previous results. 相似文献
93.
94.
95.
96.
由于土壤碳通量的空间异质性很强,传统的随机抽样方法无法对区域土壤碳通量进行准确估算,而多点采样需耗费大量的人力及设备成本,因此确定适当的采样点数量及分布策略对于区域土壤碳通量的测算非常重要。提出一种基于湿度空间分布特征的小尺度土壤碳通量空间采样策略:首先利用无线传感网密集测量区域的土壤湿度,根据湿度数据的空间分布特征划分监测区域,通过Hammond Mc Cullagh方程计算各子区域内的最优采样点数量,最终确定整个监测区域的空间采样点部署策略。提出的方法考虑了各子区域间土壤碳通量空间分布的差异,使得采样点的部署位置与土壤碳通量的分布具有较好的相关性。研究结果证明:土壤碳通量部署策略能够获得比均匀部署策略、随机部署策略更高的区域土壤碳通量估算准确度。 相似文献
97.
Two sediment sampling campaigns were conducted in 1978 and 1988 in Lake Geneva (Switzerland). Organic carbon, total nitrogen, total phosphorus and its various forms were analyzed. Results indicate a stability of organic carbon and nitrogen mass, and a significant increase of phosphorus. The variation of phosphorus mass is related to the increase of nonapatite inorganic phosphorus. This study attempts to quantify the phosphorus exchanges at the water sediment interface. The dissolved oxygen level in the bottom water determines the exchange direction. In aerobic conditions, sediments accumulate the excess of phosphorus, while in anaerobic conditions, they constitute an internal source. 相似文献
98.
Hideki Fukuda Yuji Turugida Takahiro Nakajima Eiji Nomura Akihiko Kondo 《Biotechnology letters》1996,18(8):951-956
Summary Production of phospholipase D (PLD) by Streptoverticillium cinnamoneum immobilized within porous particles was investigated in repeated batch fermentation. The enzyme productivity in repeated batch fermentation was 2.2-fold that obtained in batch fermentation without immobilization, since many of the immobilized cells could be utilized as seed cells for each subsequent batch cycle. 相似文献
99.
Mari Kawaji Shingo Kaneko Ryunosuke Tateno Yuji Isagi Tsuyoshi Yoneda 《Conservation Genetics》2009,10(4):1049-1051
Quercus miyagii is an endemic tree species in the Ryukyu Islands, Japan. We isolated and characterized 15 microsatellite loci in this species.
The number of alleles ranged from 2 to 16 and expected heterozygosities from 0.07 to 0.92. This set of markers is potentially
useful to investigate the genetic structure, gene flow, and the biogeographic history of Q. miyagii in the Ryukyu Islands, Japan. 相似文献
100.
Kiyoshi Takahashi Tadashi Yoshino Tadaatsu Akagi Katsuya Miyatani Kazuhiko Hayashi Hiroshi Sonobe Yuji Ohtsuki 《Virchows Archiv. B, Cell pathology including molecular pathology》1990,59(1):159-164
In order to clarify the function of human S100β- positive T-cells, S100β-positive T-leukemia cells (S100β TLC) were examined in vitro. S100β TLC were obtained from the peripheral blood of a patient with S100β-positive T-cell leukemia and enriched by an E-rosetting method. Two dimensional flow cytometric analysis indicated that the
vast majority of the E-positive fraction were S100β TLC expressing CD3 and CD8 antigens. Although S100β TLC expressed CD3 antigen, they were negative for the α/β and γ/δ T-cell antigen receptor (TCR) defined by monoclonal antibodies
(mabs) WT-31 and δ TCS-1, respectively. It was speculated that S100β TLC initially expressed α/β TCR but lost it during malignant transformation. When S100β TLC were cultured for 24 h, they acquired cytotoxic activity towards various NK-sensitive cell lines including K-562, Molt-3
and CEM-CCLF, but did not exhibit lysing activity towards NK-resistant cell lines including Raji, Daudi and MT-1. Despite
the NK-activity of cultured S100β TLC, they lacked the morphological features of large granular lymphocytes (LGL). S100β TLC did not exhibit lymphokine-activated killer (LAK) activity. When S100β TLC were cocultivated with NK-sensitive cells or NK-resistant cells, they selectively bound to NK-sensitive cells, indicating
that they lysed target cells by cell-to-cell contact. The finding that S100 β TLC lacked TCR molecules and their NK activity
was not inhibited by mabs reactive with the CD3-TCR complex indicated that the CD3-TCR complex was not involved in their target
recognition. These findings suggest that S100 β-positive T-cells are functionally similar to NK cells. We discuss the roles
of S100 β-positive T-cells in the human immune system. 相似文献