全文获取类型
收费全文 | 1090篇 |
免费 | 98篇 |
国内免费 | 88篇 |
出版年
2023年 | 14篇 |
2022年 | 23篇 |
2021年 | 52篇 |
2020年 | 35篇 |
2019年 | 38篇 |
2018年 | 37篇 |
2017年 | 31篇 |
2016年 | 45篇 |
2015年 | 61篇 |
2014年 | 56篇 |
2013年 | 71篇 |
2012年 | 89篇 |
2011年 | 85篇 |
2010年 | 33篇 |
2009年 | 48篇 |
2008年 | 50篇 |
2007年 | 39篇 |
2006年 | 54篇 |
2005年 | 31篇 |
2004年 | 22篇 |
2003年 | 25篇 |
2002年 | 33篇 |
2001年 | 26篇 |
2000年 | 30篇 |
1999年 | 15篇 |
1998年 | 16篇 |
1997年 | 38篇 |
1996年 | 31篇 |
1995年 | 21篇 |
1994年 | 15篇 |
1993年 | 21篇 |
1992年 | 18篇 |
1991年 | 8篇 |
1990年 | 3篇 |
1989年 | 10篇 |
1988年 | 5篇 |
1987年 | 6篇 |
1986年 | 8篇 |
1985年 | 5篇 |
1984年 | 5篇 |
1983年 | 5篇 |
1982年 | 6篇 |
1981年 | 2篇 |
1980年 | 2篇 |
1979年 | 2篇 |
1978年 | 2篇 |
1966年 | 1篇 |
1965年 | 1篇 |
1946年 | 2篇 |
排序方式: 共有1276条查询结果,搜索用时 15 毫秒
81.
Ren Z Li A Shastry BS Padma T Ayyagari R Scott MH Parks MM Kaiser-Kupfer MI Hejtmancik JF 《Human genetics》2000,106(5):531-537
A seven-generation family with 30 members affected by highly variable autosomal dominant zonular pulverulent cataracts has been previously described. We have localized the cataracts to a 19-cM interval on chromosome 2q33-q35 including the gamma-crystallin gene cluster. Maximum lod scores are 4.56 (theta=0.02) with D2S157, 3.66 (theta=0.12) with D2S72, and 3.57 (theta=0.052) with CRYG. Sequencing and allele-specific oligonucleotide analysis of the pseudo gammaE-crystallin promoter region from individuals in the pedigree suggest that activation of the gammaE-crystallin pseudo gene is unlikely to cause the cataracts in the family. In addition, base changes in the TATA box but not the Sp1-binding site have been found in unaffected controls and can be excluded as a sole cause of cataracts. In order to investigate the underlying genetic mechanism of cataracts in this family further, exons of the highly expressed gammaC- and gammaD-crystallin genes have been sequenced. The gammaD-crystallin gene shows no abnormalities, but a 5-bp duplication within exon 2 of the gammaC-crystallin gene has been found in one allele of each affected family member and is absent from both unaffected family members and unaffected controls. This mutation disrupts the reading frame of the gammaC-crystallin coding sequence and is predicted to result in the synthesis of an unstable gammaC-crystallin with 38 amino acids of the first "Greek key" motif followed by 52 random amino acids. This finding suggests that the appropriate association of mutant betagamma-crystallins into oligomers is not necessary to cause cataracts and may give us new insights into the genetic mechanism of cataract formation. 相似文献
82.
Kuang R Epp JB Ruan S Chong LS Venkataraman R Tu J He S Truong TM Groutas WC 《Bioorganic & medicinal chemistry》2000,8(5):1005-1016
A series of carboxylate derivatives based on the 1,2,5-thiadiazolidin-3-one 1,1 dioxide and isothiazolidin-3-one 1,1 dioxide scaffolds has been synthesized and the inhibitory profile of these compounds toward human leukocyte elastase (HLE), cathepsin G (Cat G) and proteinase 3 (PR 3) was then determined. Most of the compounds were found to be potent, time-dependent inhibitors of elastase, with some of the compounds exhibiting k(inact)/K1 values as high as 4,928,300 M(-1) s(-1). The inhibitory potency of carboxylate derivatives based on the 1,2,5-thiadiazolidin-3-one 1,1 dioxide platform was found to be influenced by both the pKa and the inherent structure of the leaving group. Proper selection of the primary specificity group (R(I)) was found to lead to selective inhibition of HLE over Cat G, however, those compounds that inhibited HLE also inhibited PR 3, albeit less efficiently. The predictable mode of binding of these compounds suggests that, among closely-related serine proteases, highly selective inhibitors of a particular serine protease can be fashioned by exploiting subtle differences in their S' subsites. This study has also demonstrated that the degradative action of elastase on elastin can be abrogated in the presence of inhibitor 17. 相似文献
83.
一株猴泡沫病毒野毒Pol基因的cDNA的直接测序 总被引:1,自引:0,他引:1
A 377 Kunming cell line of Rhesus Monkey Kidney (RMK) from
Centre for Medical Pr imates was amplified the cDNA fragments of the pol gene by
Nested-PCR,which of a natured infected SFV showed typical CPE after cultured for three
weeks,sequence s of products position(nt 5989-6343)were determined directly.The result
indicate d that the nucleotid sequences in the region had 48 nucleotids difference(10.78%
) between SFV infected cell and SFV-1 in GENE BANK,and there was 45 nucleotides
difference(10.11%) compared with SFVmac in the region, the test with VspⅠ showe d aligment. 相似文献
84.
Plant reproduction under spaceflight conditions has been problematic in the past. In order to determine what aspect of reproductive development is affected by microgravity, we studied pollination and embryo development in Brassica rapa L. during 16 d in microgravity on the space shuttle (STS-87). Brassica is self-incompatible and requires mechanical transfer of pollen. Short-duration access to microgravity during parabolic flights on the KC-135A aircraft was used initially to confirm that equal numbers of pollen grains could be collected and transferred in the absence of gravity. Brassica was grown in the Plant Growth Facility flight hardware as follows. Three chambers each contained six plants that were 13 d old at launch. As these plants flowered, thin colored tape was used to indicate the date of hand pollination, resulting in silique populations aged 8-15 d postpollination at the end of the 16-d mission. The remaining three chambers contained dry seeds that germinated on orbit to produce 14-d-old plants just beginning to flower at the time of landing. Pollen produced by these plants had comparable viability (93%) with that produced in the 2-d-delayed ground control. Matched-age siliques yielded embryos of equivalent developmental stage in the spaceflight and ground control treatments. Carbohydrate and protein storage reserves in the embryos, assessed by cytochemical localization, were also comparable. In the spaceflight material, growth and development by embryos rescued from siliques 15 d after pollination lagged behind the ground controls by 12 d; however, in the subsequent generation, no differences between the two treatments were found. The results demonstrate that while no stage of reproductive development in Brassica is absolutely dependent upon gravity, lower embryo quality may result following development in microgravity. 相似文献
85.
Gravity independence of seed-to-seed cycling in Brassica rapa 总被引:2,自引:0,他引:2
Musgrave ME Kuang A Xiao Y Stout SC Bingham GE Briarty LG Levenskikh MA Sychev VN Podolski IG 《Planta》2000,210(3):400-406
Growth of higher plants in the microgravity environment of orbital platforms has been problematic. Plants typically developed
more slowly in space and often failed at the reproductive phase. Short-duration experiments on the Space Shuttle showed that
early stages in the reproductive process could occur normally in microgravity, so we sought a long-duration opportunity to
test gravity's role throughout the complete life cycle. During a 122-d opportunity on the Mir space station, full life cycles
were completed in microgravity with Brassica rapa L. in a series of three experiments in the Svet greenhouse. Plant material was preserved in space by chemical fixation, freezing,
and drying, and then compared to material preserved in the same way during a high-fidelity ground control. At sampling times
13 d after planting, plants on Mir were the same size and had the same number of flower buds as ground control plants. Following
hand-pollination of the flowers by the astronaut, siliques formed. In microgravity, siliques ripened basipetally and contained
smaller seeds with less than 20% of the cotyledon cells found in the seeds harvested from the ground control. Cytochemical
localization of storage reserves in the mature embryos showed that starch was retained in the spaceflight material, whereas
protein and lipid were the primary storage reserves in the ground control seeds. While these successful seed-to-seed cycles
show that gravity is not absolutely required for any step in the plant life cycle, seed quality in Brassica is compromised by development in microgravity.
Received: 3 August 1999 / Accepted: 27 August 1999 相似文献
86.
Triterpenoids and Flavonoids from the Leaves of Astragalus membranaceus and Their Inhibitory Effects on Nitric Oxide Production 下载免费PDF全文
Zhi‐Bin Wang Ya‐Dong Zhai Zhen‐Ping Ma Chun‐Juan Yang Rong Pan Jia‐Li Yu Qiu‐Hong Wang Bing‐You Yang Hai‐Xue Kuang 《化学与生物多样性》2015,12(10):1575-1584
Four new cycloartane triterpenes, named huangqiyegenins V and VI and huangqiyenins K and L ( 1 – 4 , resp.), together with nine known triterpenoids, 5 – 13 , and eight flavonoids, 14 – 21 , were isolated from a 70%‐EtOH extract of Astragalus membranaceus leaves. The structures of the new compounds were elucidated by detailed spectroscopic analyses, and the compounds were identified as (9β,11α,16β,20R,24S)‐11,16,25‐trihydroxy‐20,24‐epoxy‐9,19‐cyclolanostane‐3,6‐dione ( 1 ), (9β,16β,24S)‐16,24,25‐trihydroxy‐9,19‐cyclolanostane‐3,6‐dione ( 2 ), (3β,6α,9β,16β,20R,24R)‐16,25‐dihydroxy‐3‐(β‐D ‐xylopyranosyloxy)‐20,24‐epoxy‐9,19‐cyclolanostan‐6‐yl acetate ( 3 ), and (3β,6α,9β,16β,24E)‐26‐(β‐D ‐glucopyranosyloxy)‐16‐hydroxy‐3‐(β‐D ‐xylopyranosyloxy)‐9,19‐cyclolanost‐24‐en‐6‐yl acetate ( 4 ). All isolated compounds were evaluated for their inhibitory activities against LPS‐induced NO production in RAW264.7 macrophage cells. Compounds 1 – 3, 14, 15 , and 18 exhibited strong inhibition on LPS‐induced NO release by macrophages with IC50 values of 14.4–27.1 μM . 相似文献
87.
88.
MotivationThe availability of ontologies and systematic documentations of phenotypes and their genetic associations has enabled large-scale network-based global analyses of the association between the complete collection of phenotypes (phenome) and genes. To provide a fundamental understanding of how the network information is relevant to phenotype-gene associations, we analyze the circular bigraphs (CBGs) in OMIM human disease phenotype-gene association network and MGI mouse phentoype-gene association network, and introduce a bi-random walk (BiRW) algorithm to capture the CBG patterns in the networks for unveiling human and mouse phenome-genome association. BiRW performs separate random walk simultaneously on gene interaction network and phenotype similarity network to explore gene paths and phenotype paths in CBGs of different sizes to summarize their associations as predictions.ResultsThe analysis of both OMIM and MGI associations revealed that majority of the phenotype-gene associations are covered by CBG patterns of small path lengths, and there is a clear correlation between the CBG coverage and the predictability of the phenotype-gene associations. In the experiments on recovering known associations in cross-validations on human disease phenotypes and mouse phenotypes, BiRW effectively improved prediction performance over the compared methods. The constructed global human disease phenome-genome association map also revealed interesting new predictions and phenotype-gene modules by disease classes. 相似文献
89.
Attenuation of microRNA‐16 derepresses the cyclins D1, D2 and E1 to provoke cardiomyocyte hypertrophy 下载免费PDF全文
90.