全文获取类型
收费全文 | 9137篇 |
免费 | 1404篇 |
国内免费 | 2724篇 |
出版年
2024年 | 16篇 |
2023年 | 312篇 |
2022年 | 336篇 |
2021年 | 480篇 |
2020年 | 549篇 |
2019年 | 720篇 |
2018年 | 549篇 |
2017年 | 534篇 |
2016年 | 516篇 |
2015年 | 462篇 |
2014年 | 562篇 |
2013年 | 690篇 |
2012年 | 427篇 |
2011年 | 527篇 |
2010年 | 400篇 |
2009年 | 571篇 |
2008年 | 535篇 |
2007年 | 602篇 |
2006年 | 598篇 |
2005年 | 457篇 |
2004年 | 347篇 |
2003年 | 362篇 |
2002年 | 327篇 |
2001年 | 281篇 |
2000年 | 275篇 |
1999年 | 214篇 |
1998年 | 175篇 |
1997年 | 145篇 |
1996年 | 115篇 |
1995年 | 112篇 |
1994年 | 128篇 |
1993年 | 101篇 |
1992年 | 91篇 |
1991年 | 79篇 |
1990年 | 84篇 |
1989年 | 66篇 |
1988年 | 47篇 |
1987年 | 55篇 |
1986年 | 44篇 |
1985年 | 81篇 |
1984年 | 47篇 |
1983年 | 33篇 |
1982年 | 54篇 |
1981年 | 27篇 |
1980年 | 25篇 |
1979年 | 29篇 |
1978年 | 17篇 |
1977年 | 24篇 |
1975年 | 9篇 |
1973年 | 8篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
1.
2.
After a 2 h exposure of intact soybean nodules to high concentrations of NaCl (100mol m?3) or oxygen (8OkPa O2), morphometric computations carried out using an image analysis technique on semi-thin sections showed that both treatments induced a decrease in the area of the inner-cortex cells, which were then characterized by a tangential elongation. In contrast, no significant change in area occurred in the middle-cortex cells although their elongation decreased. Electron microscopic observations showed that in the inner-cortex cells changes included the presence of wall infoldings, an enlarged periplasmic space and a lobate nucleus whose chromatin distribution differed from that of the control. Structural changes also occurred in the endoplasmic reticulum, microbodies, mitochondria and plastids. From several of these changes, which are similar to those noted in osmocontractil cells in response to external stimuli, it can be hypothesized that the inner cortex may provide a potential mechanism for the control of oxygen diffusion through the nodules. 相似文献
3.
4.
《Neurochemistry international》1995,26(6):635-641
Acetylcholine synthesis from radiolabelled glucose was monitored in cerebral cortex cells isolated from brains of suckling and adult rats. Acetylcholine synthesis was found much higher in suckling animals, both in the absence and presence of acetylcholinesterase (acetylcholine hydrolase, EC 3.1.1.7) inhibitor, paraoxon. Together with choline (20 μM), carnitine was found to stimulate acetylcholine synthesis in a synergistic way in cortex cells from adult rats (18%). Choline, however, was incapable of reversing an inhibitory effect exerted by carnitine on acetylcholine synthesis in cortex cells from suckling animals. Distribution of carnitine derivatives was found significantly different in the cells from young and old animals, the content of acetylcarnitine decreased with age with a corresponding increase of free carnitine. The observed differences in carnitine effect on acetylcholine synthesis suggested that high acetylcarnitine in cells capable of β-oxidation might be correlated with the lower level of acetylcholine synthesis. 相似文献
5.
《Bioorganic & medicinal chemistry》2020,28(24):115819
The exploitation of GLU988 and LYS903 residues in PARP1 as targets to design isoquinolinone (I & II) and naphthyridinone (III) analogues is described. Compounds of structure I have good biochemical and cellular potency but suffered from inferior PK. Constraining the linear propylene linker of structure I into a cyclopentene ring (II) offered improved PK parameters, while maintaining potency for PARP1. Finally, to avoid potential issues that may arise from the presence of an anilinic moiety, the nitrogen substituent on the isoquinolinone ring was incorporated as part of the bicyclic ring. This afforded a naphthyridinone scaffold, as shown in structure III. Further optimization of naphthyridinone series led to identification of a novel and highly potent PARP1 inhibitor 34, which was further characterized as preclinical candidate molecule. Compound 34 is orally bioavailable and displayed favorable pharmacokinetic (PK) properties. Compound 34 demonstrated remarkable antitumor efficacy both as a single-agent as well as in combination with chemotherapeutic agents in the BRCA1 mutant MDA-MB-436 breast cancer xenograft model. Additionally, compound 34 also potentiated the effect of agents such as temozolomide in breast cancer, pancreatic cancer and Ewing’s sarcoma models. 相似文献
6.
N. D. De With 《Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology》1996,166(5):337-343
InLymnaea stagnalis, oral uptake of ambient medium was studied using51Cr-ethylenediaminetetra-acetic acid. In normal snails Cr-ethylenediaminetetra-acetic acid uptake showed two components: a
high uptake rate within the first hour followed by moderate uptake proportional with time. The tracer accumulated mainly in
the digestive system. All animals showed initial, transient uptake. Moderate uptake proportional with time did not occur in
snails in which the buccal ganglia had been extirpated, in which both the buccal ganglia had been extirpated and the oesophagus
was sectioned, or in snails provided with an oesophageal fistula. These snails did not accumulate tracer in the intestinal
system. This type of tracer accumulation clearly represented oral ingestion of surrounding water. The oral water ingestion
rate ranged from 8 to 12 μl·h−1·g−1. Assuming complete absorption, this accounts for 20–30% of the urine production rate. At low external concentrations the
contribution of oral water ingestion to Na+ balance is negligible. However, its importance will grow with increasing external concentrations and becomes a major factor
at higher concentrations. The ingestion rate increased almost sixfold when starving snails were allowed to feed. It is suggested
that oral water ingestion is a consequence of making bite cycles and swallowing. 相似文献
7.
8.
9.
10.
《Current biology : CB》2020,30(18):3580-3590.e7