全文获取类型
收费全文 | 6721篇 |
免费 | 616篇 |
国内免费 | 7篇 |
专业分类
7344篇 |
出版年
2023年 | 48篇 |
2022年 | 106篇 |
2021年 | 262篇 |
2020年 | 124篇 |
2019年 | 162篇 |
2018年 | 164篇 |
2017年 | 151篇 |
2016年 | 248篇 |
2015年 | 422篇 |
2014年 | 438篇 |
2013年 | 423篇 |
2012年 | 614篇 |
2011年 | 590篇 |
2010年 | 338篇 |
2009年 | 275篇 |
2008年 | 447篇 |
2007年 | 334篇 |
2006年 | 324篇 |
2005年 | 291篇 |
2004年 | 266篇 |
2003年 | 243篇 |
2002年 | 203篇 |
2001年 | 52篇 |
2000年 | 56篇 |
1999年 | 49篇 |
1998年 | 41篇 |
1997年 | 39篇 |
1996年 | 29篇 |
1995年 | 25篇 |
1994年 | 26篇 |
1993年 | 20篇 |
1992年 | 30篇 |
1991年 | 25篇 |
1990年 | 28篇 |
1989年 | 39篇 |
1988年 | 26篇 |
1987年 | 47篇 |
1986年 | 24篇 |
1985年 | 20篇 |
1984年 | 25篇 |
1983年 | 21篇 |
1982年 | 18篇 |
1979年 | 19篇 |
1977年 | 15篇 |
1976年 | 19篇 |
1975年 | 16篇 |
1974年 | 15篇 |
1973年 | 15篇 |
1972年 | 14篇 |
1971年 | 15篇 |
排序方式: 共有7344条查询结果,搜索用时 15 毫秒
991.
Mariella Si?a Rachel C. Wood Enrique Saldarriaga Joshua Lawler Joseph Zunt Patricia Garcia César Cárcamo 《PloS one》2016,11(1)
Climate change poses multiple risks to the population of Lima, the largest city and capital of Peru, located on the Pacific coast in a desert ecosystem. These risks include increased water scarcity, increased heat, and the introduction and emergence of vector-borne and other climate sensitive diseases. To respond to these threats, it is necessary for the government, at every level, to adopt more mitigation and adaptation strategies. Here, focus groups were conducted with representatives from five Lima municipalities to determine priorities, perception of climate change, and decision-making processes for implementing projects within each municipality. These factors can affect the ability and desire of a community to implement climate change adaptation and mitigation strategies. The results show that climate change and other environmental factors are of relatively low priority, whereas public safety and water and sanitation services are of highest concern. Perhaps most importantly, climate change is not well understood among the municipalities. Participants had trouble distinguishing climate change from other environmental issues and did not fully understand its causes and effects. Greater understanding of what climate change is and why it is important is necessary for it to become a priority for the municipalities. Different aspects of increased climate change awareness seem to be connected to having experienced extreme weather events, whether related or not to climate change, and to higher socioeconomic status. 相似文献
992.
993.
994.
Joshua E. Johnson Terence E. McIff Phil Lee E. Bruce Toby 《Computer methods in biomechanics and biomedical engineering》2014,17(4):378-387
This study was undertaken to assess magnetic resonance imaging (MRI)-based radiocarpal surface contact models of functional loading in a clinical MRI scanner for future in vivo studies, by comparison with experimental measures from three cadaver forearm specimens. Experimental data were acquired using a Tekscan sensor during simulated light grasp. Magnetic resonance (MR) images were used to obtain model geometry and kinematics (image registration). Peak contact pressures (PPs) and average contact pressures (APs), contact forces and contact areas were determined in the radiolunate and radioscaphoid joints. Contact area was also measured directly from MR images acquired with load and compared with model data. Based on the validation criteria (within 25% of experimental data), out of the six articulations (three specimens with two articulations each), two met the criterion for AP (0%, 14%); one for peak pressure (20%); one for contact force (5%); four for contact area with respect to experiment (8%, 13%, 19% and 23%), and three contact areas met the criterion with respect to direct measurements (14%, 21% and 21%). Absolute differences between model and experimental PPs were reasonably low (within 2.5 MPa). Overall, the results indicate that MRI-based models generated from 3T clinical MR scanner appear sufficient to obtain clinically relevant data. 相似文献
995.
996.
Joshua J. LeMonte Von D. Jolley Jeffrey S. Summerhays Richard E. Terry Bryan G. Hopkins 《PloS one》2016,11(1)
Polymer coated urea (PCU) is a N fertilizer which, when added to moist soil, uses temperature-controlled diffusion to regulate N release in matching plant demand and mitigate environmental losses. Uncoated urea and PCU were compared for their effects on gaseous (N2O and NH3) and aqueous (NO3-) N environmental losses in cool season turfgrass over the entire PCU N-release period. Field studies were conducted on established turfgrass sites with mixtures of Kentucky bluegrass (Poa pratensis L.) and perennial ryegrass (Lolium perenne L.) in sand and loam soils. Each study compared 0 kg N ha-1 (control) to 200 kg N ha-1 applied as either urea or PCU (Duration 45CR®). Application of urea resulted in 127–476% more evolution of measured N2O into the atmosphere, whereas PCU was similar to background emission levels from the control. Compared to urea, PCU reduced NH3 emissions by 41–49% and N2O emissions by 45–73%, while improving growth and verdure compared to the control. Differences in leachate NO3- among urea, PCU and control were inconclusive. This improvement in N management to ameliorate atmospheric losses of N using PCU will contribute to conserving natural resources and mitigating environmental impacts of N fertilization in turfgrass. 相似文献
997.
Nicholas Boire Sean Zhang Joshua Khuvis Rick Lee Jennifer Rivers Philip Crandall M. Kevin Keel Nicole Parrish 《PloS one》2016,11(2)
The causative agent of White-nose Syndrome (WNS), Pseudogymnoascus destructans, has been shown to be fatal to several species of bats in North America. To date, no compounds or chemical control measures have been developed which eliminates the growth of the fungus in the environment or in affected animals. In the current study, we evaluated the activity of cold-pressed, terpeneless orange oil (CPT) against multiple isolates of P. destructans in vitro. For all assays, a modified Kirby-Bauer disk diffusion assay was used. Standardized spore suspensions were prepared, adjusted to a specific optical density, and used to plate fungal lawns. Plates were incubated at either 15°C or 4°C for up to 6 months and checked at regular intervals for growth. Once controls had grown, zones of inhibition were measured (mm) on test plates and compared to those obtained using current antifungal drugs. All P. destructans isolates were completely inhibited by 100% CPT (10 μL) at 1 month of incubation regardless of temperature (4°C and 15°C). Complete inhibition persisted up to 6 months following a single exposure at this concentration. Of the standard antifungals, only amphotericin B demonstrated any activity, resulting in zone diameters ranging from 58 mm to 74 mm. CPT, at the highest concentration tested (100%), had no significant effect against a variety of other environmental organisms including various filamentous fungi, bacteria and aerobic actinomycetes. Given that CPT is relatively non-toxic, the possibility exists that the all-natural, mixture could be used as an environmental pre-treatment to eradicate P. destructans from bat habitats. Additional studies are needed to assess any undesirable effects of CPT on bat behavior and health and overall impacts on other members of the interconnected ecosystem(s). 相似文献
998.
The kinetics of refolding of ribonuclease A were monitored by the return of catalytic activity and inhibitor binding at -15 degrees C in 35% methanol cryosolvent at pH* 3.0 and 6.0. Catalytic activity was measured with cytidine 2',3'-cyclic monophosphate as substrate; inhibitor binding was determined with the competitive inhibitor cytidine 2'-monophosphate. Biphasic kinetics were observed at pH* 3.0 for both return of catalytic activity and inhibitor binding. At pH* 6.0 the rate of return of catalytic activity was monophasic, whereas that of inhibitor binding was biphasic. For both inhibitor binding and catalytic activity one of the observed rates was pH-dependent. Full return of catalytic activity was obtained at the completion of the refolding process. The observations are interpreted in terms of two parallel pathways of refolding for slow-refolding ribonuclease, with several native-like, partially folded intermediate states on the minor slow-refolding pathway. Of particular note is the presence of at least one such species that has inhibitor-binding capacity but not catalytic activity. This may be rationalized in terms of the known native structure. In addition, an intermediate is postulated which has the incorrect Pro-93 conformation and only partial catalytic activity (42% of the native). The slowest observed transient is attributed to the isomerization of this proline residue and return of full catalytic activity. 相似文献
999.
N E Fink de Cabutti M Caron R Joubert M T Elola D Bladier J Herkovitz 《FEBS letters》1987,223(2):330-334
Soluble extracts of Bufo ovaries agglutinate sialidase-treated rabbit erythrocytes. Unlike other amphibian lectins this agglutination activity does not require the presence of calcium ions. It is specifically inhibited by D-galactose and its derivatives. Thiodi-D-galactoside is the most potent saccharide inhibitor followed by lactose and methyl-beta-D-galactoside, respectively. D-Fucose, D-glucose and D-mannose do not inhibit the activity at concentrations at or above 100 mM. The lectin has been purified 500-fold to apparent homogeneity from the ovaries by salt extraction and affinity chromatography on lactose-aminophenyl-agarose, with a yield of about 0.2%. The molecular mass determined by gel filtration under native conditions was 30 kDa; polyacrylamide gel electrophoresis in SDS gave a molecular mass of 15 kDa, suggesting that the lectin is a dimer. The lectin has an isoelectric point of 40 and contains a high proportion of acidic amino acids. 相似文献
1000.