全文获取类型
收费全文 | 981篇 |
免费 | 10篇 |
国内免费 | 34篇 |
专业分类
系统科学 | 20篇 |
丛书文集 | 2篇 |
教育与普及 | 3篇 |
理论与方法论 | 12篇 |
现状及发展 | 206篇 |
研究方法 | 131篇 |
综合类 | 625篇 |
自然研究 | 26篇 |
出版年
2021年 | 4篇 |
2020年 | 5篇 |
2019年 | 5篇 |
2018年 | 14篇 |
2017年 | 12篇 |
2016年 | 8篇 |
2015年 | 13篇 |
2014年 | 18篇 |
2013年 | 18篇 |
2012年 | 67篇 |
2011年 | 95篇 |
2010年 | 37篇 |
2009年 | 24篇 |
2008年 | 52篇 |
2007年 | 66篇 |
2006年 | 52篇 |
2005年 | 63篇 |
2004年 | 39篇 |
2003年 | 64篇 |
2002年 | 53篇 |
2001年 | 40篇 |
2000年 | 42篇 |
1999年 | 20篇 |
1996年 | 4篇 |
1992年 | 10篇 |
1991年 | 7篇 |
1990年 | 4篇 |
1989年 | 10篇 |
1988年 | 9篇 |
1987年 | 9篇 |
1986年 | 5篇 |
1985年 | 9篇 |
1982年 | 6篇 |
1981年 | 7篇 |
1980年 | 8篇 |
1979年 | 8篇 |
1978年 | 7篇 |
1977年 | 10篇 |
1976年 | 5篇 |
1975年 | 9篇 |
1974年 | 5篇 |
1973年 | 9篇 |
1972年 | 3篇 |
1971年 | 9篇 |
1970年 | 9篇 |
1969年 | 7篇 |
1968年 | 5篇 |
1967年 | 7篇 |
1966年 | 5篇 |
1965年 | 7篇 |
排序方式: 共有1025条查询结果,搜索用时 0 毫秒
21.
Postmitochondrial supernatants prepared from livers of mice, rats, rabbits, dogs, and monkeys metabolized 2,4-dinitrotulene. The pattern of metabolites was characterized in both sexes of the species examined. In addition, the pattern of metabolites was altered by varying incubation conditions and pretreating male rats with phenobarbital or SKF 525-A. 相似文献
22.
23.
24.
For analysts there is a tradeoff between the accuracy and the timeliness of their forecasts. Prior literature heavily investigates analyst forecast accuracy. Few papers investigate the importance of timeliness. To our best knowledge, there are no empirical papers to date to investigate the dynamic interplay between these key characteristics. We show that if analysts experience a period of high accuracy relative to their peers, they subsequently focus more on the timeliness of their forecasts in the subsequent period and thus issue their forecasts earlier than they did in the prior period. Copyright © 2016 John Wiley & Sons, Ltd. 相似文献
25.
26.
Chromosome integrity in response to chemically or radiation-induced chromosome breaks and the perturbation of ongoing replication
forks relies on multiple DNA repair mechanisms. However, repair of these lesions may lead to unwanted chromosome rearrangement
if not properly executed or regulated. As these types of chromosomal alterations threaten the cell’s and the organism’s very
own survival, multiple systems are developed to avoid or at least limit break-induced chromosomal rearrangements. In this
review, we highlight cellular strategies for repressing DNA break-induced chromosomal translocations in multiple model systems
including yeast, mouse, and human. These pathways select proper homologous templates or broken DNA ends for the faithful repair
of DNA breaks to avoid undesirable chromosomal translocations. 相似文献
27.
Rakesh K. Sahoo Arya Das Saurabh Singh Damin Lee Saroj K. Singh Rajaram S. Mane Je Moon Yun Kwang Ho Kim 《自然科学进展(英文版)》2019,29(4):410-415
A 3D porous carbon-manganese oxide ([email protected]) nanocomposite is successfully synthesized via a thermal plasma deposition method. The chemical bonds and compositions, phase structures, surface morphologies, etc. of as-obtained [email protected] nanocomposite were characterized by the various equipment, such as X-ray diffractometer, X-ray photoelectron spectroscopy, and electron microscopes. The electrochemical performances of the [email protected] nanocomposite electrode showed a specific capacitance of 780 F g?1 at a current density of 2 A g?1 and a capacitance retention rate of 99% after 5000 charge-discharge cycles at a high current density of 10 A g?1. These excellent capacitive performances may be attributed to the encapsulation of MnO nanoparticles by porous carbon sheets in the [email protected] MnO nanocomposite structure. It is believed that the carbon-encapsulated MnO nanoparticles can be protected from a volume deformation during the charge adsorption/desorption cycle and can be electrically improved by the encapsulated carbon sheets, resulting in better overall capacitive performance. In addition, this study also demonstrates the practical applicability by assembling a supercapacitor using the as-obtained [email protected] nanocomposite to glow a light emitting diode. 相似文献
28.
Jinwon Lim Hyo-Jung Lee Bonglee Kim Jeong-Un Choi Yoeok Shin Eun Jung Sohn Sung-Hoon Kim 《科学通报(英文版)》2014,59(25):3127-3133
Though Hongbaekjeong(HBJ),a hebal mixture of three medicinal plants,has been traditionally used for arthritis and muscular pain,its scientific evidence still remains unclear.Thus,in the present study,analgesic and anti-inflammatory mechanism of HBJ was evaluated in vitro and in vivo.HBJ significantly reduced NO production and prostaglandin E2(PGE2)release and also attenuated the expression of cyclooxygenase 2(COX-2)in lipopolysaccharides(LPS)and interferon(IFN)-c treated RAW 264.7 cells.Furthermore,HBJ abrogated the production of proinflammatory cytokines such as interleukin(IL)1b,IL-6,IL-8 and monocyte chemoattractant protein-1(MCP-1)in LPS and IFN-c treated RAW 264.7 cells.In addition,HBJ significantly decreased the number of writhing syndrome induced by acetic acid,and also increased latency in hot-plate method and tail flick test in mice.Consistently,HBJ significantly reduced the edema volume in the hind paw of the rats with arthritis induced by Freund’s complete adjuvant(FCA)compared to untreated control.Collectively,our findings demonstrate the antiinflammatory and analgesic potential of HBJ via inhibition of proinflammatory cytokines and PGE2 release for treatment of arthritis and muscular pain. 相似文献
29.
Parton LE Ye CP Coppari R Enriori PJ Choi B Zhang CY Xu C Vianna CR Balthasar N Lee CE Elmquist JK Cowley MA Lowell BB 《Nature》2007,449(7159):228-232
A subset of neurons in the brain, known as 'glucose-excited' neurons, depolarize and increase their firing rate in response to increases in extracellular glucose. Similar to insulin secretion by pancreatic beta-cells, glucose excitation of neurons is driven by ATP-mediated closure of ATP-sensitive potassium (K(ATP)) channels. Although beta-cell-like glucose sensing in neurons is well established, its physiological relevance and contribution to disease states such as type 2 diabetes remain unknown. To address these issues, we disrupted glucose sensing in glucose-excited pro-opiomelanocortin (POMC) neurons via transgenic expression of a mutant Kir6.2 subunit (encoded by the Kcnj11 gene) that prevents ATP-mediated closure of K(ATP) channels. Here we show that this genetic manipulation impaired the whole-body response to a systemic glucose load, demonstrating a role for glucose sensing by POMC neurons in the overall physiological control of blood glucose. We also found that glucose sensing by POMC neurons became defective in obese mice on a high-fat diet, suggesting that loss of glucose sensing by neurons has a role in the development of type 2 diabetes. The mechanism for obesity-induced loss of glucose sensing in POMC neurons involves uncoupling protein 2 (UCP2), a mitochondrial protein that impairs glucose-stimulated ATP production. UCP2 negatively regulates glucose sensing in POMC neurons. We found that genetic deletion of Ucp2 prevents obesity-induced loss of glucose sensing, and that acute pharmacological inhibition of UCP2 reverses loss of glucose sensing. We conclude that obesity-induced, UCP2-mediated loss of glucose sensing in glucose-excited neurons might have a pathogenic role in the development of type 2 diabetes. 相似文献
30.
Complex gas hydrate from the Cascadia margin 总被引:3,自引:0,他引:3
Lu H Seo YT Lee JW Moudrakovski I Ripmeester JA Chapman NR Coffin RB Gardner G Pohlman J 《Nature》2007,445(7125):303-306
Natural gas hydrates are a potential source of energy and may play a role in climate change and geological hazards. Most natural gas hydrate appears to be in the form of 'structure I', with methane as the trapped guest molecule, although 'structure II' hydrate has also been identified, with guest molecules such as isobutane and propane, as well as lighter hydrocarbons. A third hydrate structure, 'structure H', which is capable of trapping larger guest molecules, has been produced in the laboratory, but it has not been confirmed that it occurs in the natural environment. Here we characterize the structure, gas content and composition, and distribution of guest molecules in a complex natural hydrate sample recovered from Barkley canyon, on the northern Cascadia margin. We show that the sample contains structure H hydrate, and thus provides direct evidence for the natural occurrence of this hydrate structure. The structure H hydrate is intimately associated with structure II hydrate, and the two structures contain more than 13 different hydrocarbon guest molecules. We also demonstrate that the stability field of the complex gas hydrate lies between those of structure II and structure H hydrates, indicating that this form of hydrate is more stable than structure I and may thus potentially be found in a wider pressure-temperature regime than can methane hydrate deposits. 相似文献