全文获取类型
收费全文 | 9570篇 |
免费 | 784篇 |
国内免费 | 719篇 |
专业分类
11073篇 |
出版年
2024年 | 32篇 |
2023年 | 130篇 |
2022年 | 299篇 |
2021年 | 520篇 |
2020年 | 343篇 |
2019年 | 400篇 |
2018年 | 443篇 |
2017年 | 287篇 |
2016年 | 414篇 |
2015年 | 608篇 |
2014年 | 683篇 |
2013年 | 672篇 |
2012年 | 865篇 |
2011年 | 802篇 |
2010年 | 443篇 |
2009年 | 394篇 |
2008年 | 470篇 |
2007年 | 378篇 |
2006年 | 357篇 |
2005年 | 302篇 |
2004年 | 244篇 |
2003年 | 186篇 |
2002年 | 180篇 |
2001年 | 181篇 |
2000年 | 155篇 |
1999年 | 170篇 |
1998年 | 79篇 |
1997年 | 88篇 |
1996年 | 74篇 |
1995年 | 90篇 |
1994年 | 87篇 |
1993年 | 58篇 |
1992年 | 88篇 |
1991年 | 78篇 |
1990年 | 69篇 |
1989年 | 45篇 |
1988年 | 55篇 |
1987年 | 37篇 |
1986年 | 42篇 |
1985年 | 53篇 |
1984年 | 26篇 |
1983年 | 17篇 |
1982年 | 21篇 |
1981年 | 11篇 |
1979年 | 11篇 |
1978年 | 14篇 |
1977年 | 10篇 |
1974年 | 11篇 |
1969年 | 5篇 |
1968年 | 8篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
221.
222.
Gluconacetobacter diazotrophicus is an N(2)-fixing endophyte isolated from sugarcane. G. diazotrophicus was grown on solid medium at atmospheric partial O(2) pressures (pO(2)) of 10, 20, and 30 kPa for 5 to 6 days. Using a flowthrough gas exchange system, nitrogenase activity and respiration rate were then measured at a range of atmospheric pO(2) (5 to 60 kPa). Nitrogenase activity was measured by H(2) evolution in N(2)-O(2) and in Ar-O(2), and respiration rate was measured by CO(2) evolution in N(2)-O(2). To validate the use of H(2) production as an assay for nitrogenase activity, a non-N(2)-fixing (Nif(-)) mutant of G. diazotrophicus was tested and found to have a low rate of uptake hydrogenase (Hup(+)) activity (0.016 +/- 0.009 micromol of H(2) 10(10) cells(-1) h(-1)) when incubated in an atmosphere enriched in H(2). However, Hup(+) activity was not detectable under the normal assay conditions used in our experiments. G. diazotrophicus fixed nitrogen at all atmospheric pO(2) tested. However, when the assay atmospheric pO(2) was below the level at which the colonies had been grown, nitrogenase activity was decreased. Optimal atmospheric pO(2) for nitrogenase activity was 0 to 20 kPa above the pO(2) at which the bacteria had been grown. As atmospheric pO(2) was increased in 10-kPa steps to the highest levels (40 to 60 kPa), nitrogenase activity decreased in a stepwise manner. Despite the decrease in nitrogenase activity as atmospheric pO(2) was increased, respiration rate increased marginally. A large single-step increase in atmospheric pO(2) from 20 to 60 kPa caused a rapid 84% decrease in nitrogenase activity. However, upon returning to 20 kPa of O(2), 80% of nitrogenase activity was recovered within 10 min, indicating a "switch-off/switch-on" O(2) protection mechanism of nitrogenase activity. Our study demonstrates that colonies of G. diazotrophicus can fix N(2) at a wide range of atmospheric pO(2) and can adapt to maintain nitrogenase activity in response to both long-term and short-term changes in atmospheric pO(2). 相似文献
223.
224.
三突花蛛对茶小绿叶蝉的捕食作用及其模拟模型的研究 总被引:10,自引:1,他引:10
在室内条件下,测定结果表明三突花株亚成蛛对茶小绿叶蝉若虫及成虫的日捕食量分别为18.3头/d,17.3头/d,对成虫的功能反应曲线可用HOllng圆盘方程模拟:Na=1.05586Nt/(1+0.01365/Nt)自身密度反应用Hassel-Varley模型拟合,E=0.517P^-0.6567,经X^2检验,以上各方程理论值与实际值误差不显著(〈P0.10)。温度(T)对功能反应的影响可用以下方 相似文献
225.
226.
Hai Jin He Xing Sheng Wang Rong Pan Liang Dong Wang Ming Nan Liu Rong Qiao He 《BMC cell biology》2009,10(1):81
Background
The microtubule-associated protein tau is able to interact with actin and serves as a cross-linker between the microtubule and actin networks. The microtubule-binding domain of tau is known to be involved in its interaction with actin. Here, we address the question of whether the other domains of tau also interact with actin. 相似文献227.
Jennifer L. Belsky Alyssa J. Ashley Premal A. Bhatt Karen V. Gilbert Heather R. Joyce Chunhua Pan Horacio Pappa Samir Z. Wahab 《AAPS PharmSciTech》2010,11(2):994-1004
The water-insoluble procedures in US Pharmacopeia (USP) General Chapter Residual Solvents <467>, which are based on European Pharmacopoeia procedures, were optimized and modified before their inclusion in the chapter to improve their scope, performance, and ruggedness.
The optimized procedures use a static headspace introduction system with a gas chromatograph equipped with a flame ionization
detector. This article describes some of the key changes made to the USP published procedures, including use of dimethyl sulfoxide
(DMSO) or dimethylformamide (DMF) as the solvent, addition of 5 mL of water and 1 mL of sample (dissolved in DMSO or DMF)
to the headspace vial, use of a 3:1 GC split ratio, and use of new matrix-matched system suitability solutions. These procedures
were verified with two different active pharmaceutical ingredients—hydroxyzine pamoate and prednisone. In the investigation,
the more polar material (hydroxyzine pamoate) showed greater recoveries for the optimized procedures when prepared in DMSO.
The less polar material (prednisone) typically had greater recoveries in DMF for the optimized procedures. During experimentation,
insights into sample preparation, additional types of headspace instrumentation, solvent purity, and other parameters were
also gained. 相似文献
228.
229.
230.
Cuiping Xie Feiming Ye Ning Zhang Yuxue Huang Yun Pan Xiaojie Xie 《Journal of cellular and molecular medicine》2021,25(15):7280-7293
Chemokine C-C motif ligand 7 (CCL7), a member of CC chemokine subfamily, plays pivotal roles in numerous inflammatory diseases. Hyper-activation of inflammation is an important characteristic of abdominal aortic aneurysm (AAA). Therefore, in the present study, we aimed to determine the effect of CCL7 on AAA formation. CCL7 abundance in aortic tissue and macrophage infiltration were both increased in angiotensin II (Ang II)-induced AAA mice. Ex vivo, CCL7 promoted macrophage polarization towards M1 phenotype. This effect was reversed by the blockage of CCR1, a receptor of CCL7. CCL7 up-regulated JAK2/STAT1 protein level in macrophage, and CCL7-induced M1 activation was suppressed by JAK2/STAT1 pathway inhibition. To verify the effect of CCL7 on AAA in vivo, either CCL7-neutralizing antibody (CCL7-nAb) or vehicles were intraperitoneally injected 24 hours prior to Ang II infusion and subsequently every three days for 4 weeks. CCL7-nAb administration significantly attenuated Ang II-induced luminal and external dilation as well as pathological remodelling. Immunostaining showed that CCL7-nAb administration significantly decreased aneurysmal macrophage infiltration. In conclusion, CCL7 contributed to Ang II-induced AAA by promoting M1 phenotype of macrophage through CCR1/JAK2/STAT1 signalling pathway. 相似文献