全文获取类型
收费全文 | 3863篇 |
免费 | 292篇 |
国内免费 | 584篇 |
出版年
2023年 | 59篇 |
2022年 | 71篇 |
2021年 | 99篇 |
2020年 | 105篇 |
2019年 | 127篇 |
2018年 | 159篇 |
2017年 | 116篇 |
2016年 | 111篇 |
2015年 | 113篇 |
2014年 | 182篇 |
2013年 | 293篇 |
2012年 | 181篇 |
2011年 | 155篇 |
2010年 | 151篇 |
2009年 | 188篇 |
2008年 | 193篇 |
2007年 | 168篇 |
2006年 | 128篇 |
2005年 | 142篇 |
2004年 | 158篇 |
2003年 | 107篇 |
2002年 | 150篇 |
2001年 | 111篇 |
2000年 | 125篇 |
1999年 | 95篇 |
1998年 | 86篇 |
1997年 | 82篇 |
1996年 | 68篇 |
1995年 | 74篇 |
1994年 | 75篇 |
1993年 | 87篇 |
1992年 | 74篇 |
1991年 | 69篇 |
1990年 | 53篇 |
1989年 | 26篇 |
1988年 | 32篇 |
1987年 | 33篇 |
1986年 | 24篇 |
1985年 | 52篇 |
1984年 | 41篇 |
1983年 | 39篇 |
1982年 | 58篇 |
1981年 | 44篇 |
1980年 | 41篇 |
1979年 | 33篇 |
1978年 | 36篇 |
1977年 | 37篇 |
1976年 | 36篇 |
1975年 | 23篇 |
1973年 | 14篇 |
排序方式: 共有4739条查询结果,搜索用时 78 毫秒
1.
2.
3.
4.
Summary Paleozoic carbonate ramp sedimentation has generally been described in terms of downlapping clinoforms composed of allochthonous
sediment derived from shallower environments. However, during transgressive episodes when carbonate sediment production is
low and down slope sediment transport by gravity becomes inactive, autochthonous carbonate sediment accumulates in vertical
stacks of essentially in situ sediment. Autochthonous outer ramp deposition is probably a part of many Paleozoic ramp strata,
but has heretofore not been recognized because of the general absence of adequate exposures.
Evidence of autochthonous, in situ deposition and preservation of sediments in a starved setting is well displayed in the
Alamogordo Member of the Lake Valley Formation in south central New Mexico. This evidence includes: 1) beds and bed sets that
are individually continuous and traceable along ramp slope for 32 km, 2) down-ramp sequential distributions of depth-sensitive
organisms and assemblages but patchy distribution of rock types, 3) lack of sedimentary structures indicative of transport,
4) well preserved, unabraded fossils, 5) the common occurrence of fossils in life position, 6) beds traceable into and through
mounds 7) bed thickness trends ascribed to biotic productivity, and 8) geopetal structures in original position.
Integrated paleontologic, sedimentologic, and stratigraphic data provide information about depositional processes and setting.
The depositional slope was approximately 0.5o based on the distribution of fossil algae; this is comparable to dips reported for other Mississippian homoclinal ramps.
An oxygen minimum zone may have impinged on the ramp during a major flooding event. Shifts in biotic gradients from bed to
bed reveal transgressive-regressive patterns that would not be resolvable without detailed paleontological evidence.
The Alamogordo Member formed as a result of transgressive and early highstand starved carbonate sedimentation along a narrow,
homoclinal outer ramp. The surface of maximum flooding and the boundary between the TST and HST are within the Alamogordo
Member. 相似文献
5.
《Bioorganic & medicinal chemistry》2020,28(9):115437
NDM-1 can hydrolyze nearly all available β-lactam antibiotics, including carbapenems. NDM-1 producing bacterial strains are worldwide threats. It is still very challenging to find a potent NDM-1 inhibitor for clinical use. In our study, we used a metal-binding pharmacophore (MBP) enriched virtual fragment library to screen NDM-1 hits. SPR screening helped to verify the MBP virtual hits and identified a new NDM-1 binder and weak inhibitor A1. A solution NMR study of 15N-labeled NDM-1 showed that A1 disturbed all three residues coordinating the second zinc ion (Zn2) in the active pocket of NDM-1. The perturbation only happened in the presence of zinc ion, indicating that A1 bound to Zn2. Based on the scaffold of A1, we designed and synthesized a series of NDM-1 inhibitors. Several compounds showed synergistic antibacterial activity with meropenem against NDM-1 producing K. pneumoniae. 相似文献
6.
A new species of the genus Amolops Cope,1865 is described from Xinduqiao,Kangding,Sichuan.It was previously identified as Amolops kangtingensis,which is synonymized to Amolops mantzorum in this study.The new species,Amolops xinduqiao sp.nov.,is distinguished from all other congeners by the following combination of characters:(1) medium body size,adult males SVL 41.2-47.5 mm (n=15,average 43.9 mm),adult females SVL 48.5-56.6 mm (n=15,average 52.5 mm);(2) head length equal to width or slightly wider than long;(3) tympanum small,but distinct;(4) vomerine teeth in two tiny rows,separated by a space about one vomerine teeth row;(5) bony projections on lower jaw absent;(6) dorsolateral folds usually absent;(7) tarsal folds or glands on tarsus absent;(8) circummarginal groove on disc of finger Ⅰ absent;(9) tibiotarsal articulation reaching nostril or beyond;(10) webs of toe Ⅳ reaching to distal articulation,other toes fully webbed to disc;and (11) vocal sac absent in males. 相似文献
7.
8.
9.
10.
Description of a new anaerobic thermophilic bacterium,Thermoanaerobacterium butyriciformans sp. nov.
G. López S.J. Cañas-Duarte A.M. Pinzón-Velasco N.E. Vega-Vela M. Rodríguez S. Restrepo S. Baena 《Systematic and applied microbiology》2017,40(2):86-91
Strain USBA-019T, an anaerobic and thermophilic strain, was identified as a new member of the genus Thermoanaerobacterium. USBA-019T cells are gram-positive, strictly anaerobic, thermophilic, chemoorganotrophic, moderately acidophilic, non-motile, endospore-forming, slightly curved, and rod-shaped. Cells measure 0.4 × 3.0–7.0 μm. Optimal growth occurs at 50–55 °C (35–65 °C). Optimum pH is 5.0–5.5 (4.0–8.5). Thiosulfate, elemental sulfur and nitrate were utilized as electron acceptors. Fermentation of glucose, lactose, cellobiose, galactose, arabinose, xylose, starch and xylan primarily produced acetate and butyrate. Xylan, starch and cellobiose produced ethanol and starch, cellobiose, galactose, arabinose and mannose produced lactic acid. Phylogenetic analyses based on 16S rRNA gene sequence comparison and genomic relatedness indices show the close relation of USBA-019T to Thermoanaerobacterium thermostercoris and Thermoanaerobacterium aotearoense (similarity value: 99%). Hybridization of USBA-019T, Th. thermostercoris DSM22141T and Th. aotearoense DMS10170T found DNA–DNA relatedness of 33.2% and 18.2%, respectively. Based on phenotypic, chemotaxonomic and phylogenetic evidence, along with low identity at whole genome level, USBA-019T is a novel species of the genus Thermoanaerobacterium which we propose to name Thermoanaerobacterium butyriciformans sp. nov. The type strain is USBA-019T (=CMPUJ U-019T = DSM 101588T). 相似文献