全文获取类型
收费全文 | 11383篇 |
免费 | 1062篇 |
国内免费 | 7篇 |
出版年
2021年 | 82篇 |
2018年 | 107篇 |
2017年 | 93篇 |
2016年 | 182篇 |
2015年 | 269篇 |
2014年 | 319篇 |
2013年 | 450篇 |
2012年 | 546篇 |
2011年 | 578篇 |
2010年 | 404篇 |
2009年 | 355篇 |
2008年 | 527篇 |
2007年 | 582篇 |
2006年 | 571篇 |
2005年 | 576篇 |
2004年 | 582篇 |
2003年 | 515篇 |
2002年 | 561篇 |
2001年 | 130篇 |
2000年 | 106篇 |
1999年 | 164篇 |
1998年 | 158篇 |
1997年 | 110篇 |
1996年 | 118篇 |
1995年 | 117篇 |
1994年 | 161篇 |
1993年 | 135篇 |
1992年 | 120篇 |
1991年 | 117篇 |
1990年 | 116篇 |
1989年 | 117篇 |
1988年 | 111篇 |
1987年 | 107篇 |
1986年 | 97篇 |
1985年 | 132篇 |
1984年 | 142篇 |
1983年 | 120篇 |
1982年 | 176篇 |
1981年 | 195篇 |
1980年 | 188篇 |
1979年 | 111篇 |
1978年 | 149篇 |
1977年 | 134篇 |
1976年 | 113篇 |
1975年 | 94篇 |
1974年 | 125篇 |
1973年 | 121篇 |
1972年 | 79篇 |
1970年 | 81篇 |
1969年 | 78篇 |
排序方式: 共有10000条查询结果,搜索用时 187 毫秒
1.
David Dubbeldam Sofía Calero Donald E. Ellis Randall Q. Snurr 《Molecular simulation》2016,42(2):81-101
A new software package, RASPA, for simulating adsorption and diffusion of molecules in flexible nanoporous materials is presented. The code implements the latest state-of-the-art algorithms for molecular dynamics and Monte Carlo (MC) in various ensembles including symplectic/measure-preserving integrators, Ewald summation, configurational-bias MC, continuous fractional component MC, reactive MC and Baker's minimisation. We show example applications of RASPA in computing coexistence properties, adsorption isotherms for single and multiple components, self- and collective diffusivities, reaction systems and visualisation. The software is released under the GNU General Public License. 相似文献
2.
3.
Michael J. A. Simpson Donald F. Macintosh John B. Cloughley Angus E. Stuart 《Economic botany》1996,50(1):122-129
The development ofM. gale oil as an insect repellent has created a requirement for cultivation of the plant. Botanical evidence indicates thatM. gale is likely to thrive on well—aerated acid peatland and could become a valuable crop on land of low agricultural value. Plant growth would be enhanced by the prevention of grazing and could be combined with softwood forestry since the trees would benefit from soil nitrogen enrichment thanks to the symbiotic association ofM. gale andFrankia. The economics of oil production would be improved if additional compounds of value such as pharmacologically active fiavonoids could be extracted from the by-products. 相似文献
4.
Anthropogenic N deposition increases soil organic matter accumulation without altering its biochemical composition 总被引:1,自引:0,他引:1 下载免费PDF全文
Donald R. Zak Zachary B. Freedman Rima A. Upchurch Markus Steffens Ingrid Kögel‐Knabner 《Global Change Biology》2017,23(2):933-944
Accumulating evidence indicates that future rates of atmospheric N deposition have the potential to increase soil C storage by reducing the decay of plant litter and soil organic matter (SOM). Although the microbial mechanism underlying this response is not well understood, a decline in decay could alter the amount, as well as biochemical composition of SOM. Here, we used size‐density fractionation and solid‐state 13C‐NMR spectroscopy to explore the extent to which declines in microbial decay in a long‐term (ca. 20 yrs.) N deposition experiment have altered the biochemical composition of forest floor, bulk mineral soil, as well as free and occluded particulate organic matter. Significant amounts of organic matter have accumulated in occluded particulate organic matter (~20%; oPOM); however, experimental N deposition had not altered the abundance of carboxyl, aryl, alkyl, or O/N‐alkyl C in forest floor, bulk mineral soil, or any soil fraction. These observations suggest that biochemically equivalent organic matter has accumulated in oPOM at a greater rate under experimental N deposition, relative to the ambient treatment. Although we do not understand the process by which experimental N deposition has fostered the occlusion of organic matter by mineral soil particles, our results highlight the importance of interactions among the products of microbial decay and the chemical and physical properties of silt and clay particles that occlude organic matter from microbial attack. Because oPOM can reside in soils for decades to centuries, organic matter accumulating under future rates of anthropogenic N deposition could remain in soil for long periods of time. If temperate forest soils in the Northern Hemisphere respond like those in our experiment, then unabated deposition of anthropogenic N from the atmosphere has the potential to foster greater soil C storage, especially in fine‐texture forest soils. 相似文献
5.
† Robert W. Neumar Scott M. Hagle †Donald J. DeGracia Gary S. Krause †Blaine C. White 《Journal of neurochemistry》1996,66(1):421-424
Abstract: Proteolytic degradation of numerous calpain substrates, including cytoskeletal and regulatory proteins, has been observed during brain ischemia and reperfusion. In addition, calpain inhibitors have been shown to decrease degradation of these proteins and decrease postischemic neuronal death. Although these observations support the inference of a role for μ-calpain in the pathophysiology of ischemic neuronal injury, the evidence is indirect. A direct indicator of μ-calpain proteolytic activity is autolysis of its 80-kDa catalytic subunit, and therefore we examined the μ-calpain catalytic subunit for evidence of autolysis during cerebral ischemia. Rabbit brain homogenates obtained after 0, 5, 10, and 20 min of cardiac arrest were electrophoresed and immunoblotted with a monoclonal antibody specific to the μ-calpain catalytic subunit. In nonischemic brain homogenates the antibody identified an 80-kDa band, which migrated identically with purified μ-calpain, and faint 78- and 76-kDa bands, which represent autolyzed forms of the 80-kDa subunit. The average density of the 80-kDa band decreased by 25 ± 4 ( p = 0.008) and 28 ± 9% ( p = 0.004) after 10 and 20 min of cardiac arrest, respectively, whereas the average density of the 78-kDa band increased by 111 ± 50% ( p = 0.02) after 20 min of cardiac arrest. No significant change in the density of the 76-kDa band was detected. These results provide direct evidence for autolysis of brain μ-calpain during cerebral ischemia. Further work is needed to characterize the extent, duration, and localization of μ-calpain activity during brain ischemia and reperfusion as well as its role in the causal pathway of postischemic neuronal injury. 相似文献
6.
Donald S. McLusky 《Aquatic Ecology》1993,27(2-4):489-493
The Proceedings of the ECSA 21 symposium on Marine and Estuarine Gradients are reviewed. It is emphasised that this is probably
the first time that a full set of papers on the tidal freshwater sections of estuaries has appeared. There is however some
ambiguity in the terminology applied to such waters, and a more consistent terminology is proposed. In particular the estuary
is defined as reaching upstream as far as the tidal limit, irrespective of salinity.
A wide variety of gradients within estuaries and coastal waters are considered, but it is apparent that the crucial spatial
gradients are based on salinity, oxygen and turbidity, and that many other gradients are co-variables with these parameters.
Temperature is also important for temporal gradients. 相似文献
7.
Amy L. Albrecht Seema Somji Mary Ann Sens Donald A. Sens Scott H. Garrett 《Biometals》2008,21(4):405-416
The human prostate gland undergoes a prominent alteration in Zn+2 homeostasis during the development of prostate cancer. The goal of the present study was to determine if the immortalized human prostate cell line (RWPE-1) could serve as a model system to study the role of zinc in prostate cancer. The study examined the expression of mRNA for 19 members of the zinc transporter gene family in normal prostate tissue, the prostate RWPE-1 cell line, and the LNCaP, DU-145 and PC-3 prostate cancer cell lines. The study demonstrated that the expression of the 19 zinc transporters was similar between the RWPE-1 cell line and the in situ prostate gland. Of the 19 zinc transporters, only 5 had levels that were different between the RWPE-1 cells and the tissue samples; all five being increased (ZnT-6, Zip-1, Zip-3A, Zip-10, and Zip-14). The response of the 19 transporters was also determined when the cell lines were exposed to 75 microM Zn+2 for 24 h. It was shown for the RWPE-1 cells that only 5 transporters responded to Zn+2 with mRNA for ZnT-1 and ZnT-2 being increased while mRNA for ZnT-7, Zip-7 and Zip-10 transporters were decreased. It was shown for the LNCaP, DU-145 and PC-3 cells that Zn+2 had no effect on the mRNA levels of all 19 transporters except for an induction of ZnT-1 in PC-3 cells. Overall, the study suggests that the RWPE-1 cells could be a valuable model for the study of the zinc transporter gene family in the prostate. 相似文献
8.
9.
10.