全文获取类型
收费全文 | 5711篇 |
免费 | 447篇 |
国内免费 | 7篇 |
专业分类
6165篇 |
出版年
2023年 | 20篇 |
2022年 | 38篇 |
2021年 | 86篇 |
2020年 | 52篇 |
2019年 | 77篇 |
2018年 | 87篇 |
2017年 | 96篇 |
2016年 | 157篇 |
2015年 | 243篇 |
2014年 | 290篇 |
2013年 | 371篇 |
2012年 | 398篇 |
2011年 | 387篇 |
2010年 | 243篇 |
2009年 | 274篇 |
2008年 | 351篇 |
2007年 | 328篇 |
2006年 | 352篇 |
2005年 | 318篇 |
2004年 | 335篇 |
2003年 | 308篇 |
2002年 | 296篇 |
2001年 | 78篇 |
2000年 | 70篇 |
1999年 | 87篇 |
1998年 | 68篇 |
1997年 | 42篇 |
1996年 | 43篇 |
1995年 | 43篇 |
1994年 | 44篇 |
1993年 | 41篇 |
1992年 | 56篇 |
1991年 | 36篇 |
1990年 | 34篇 |
1989年 | 36篇 |
1988年 | 38篇 |
1987年 | 35篇 |
1986年 | 32篇 |
1985年 | 27篇 |
1984年 | 29篇 |
1983年 | 25篇 |
1982年 | 22篇 |
1981年 | 17篇 |
1980年 | 22篇 |
1979年 | 16篇 |
1978年 | 12篇 |
1977年 | 19篇 |
1976年 | 13篇 |
1974年 | 12篇 |
1973年 | 11篇 |
排序方式: 共有6165条查询结果,搜索用时 0 毫秒
101.
To date, the complete genome sequences of more than 250 organisms have been determined. This information can now be used to determine whether there exist any invariant sequences that are conserved among all organisms, from bacteria to plants, animals, and humans. The existence of invariant sequences would strongly suggest that these sequences have been inherited unchanged from the last common ancestor of all life, and that they have essential functions. We have developed a new software program to identify invariant sequences conserved among the currently sequenced genomes and applied this analysis to the complete genome sequences of 266 organisms. We have identified 3 invariant DNA sequences longer than or equal to 11 bp and 6 invariant amino acid sequences longer than or equal to 6 aa. The longest invariant DNA sequence, AAGTCGTACAAGGT (15 bp), was found in the 16S/18S rRNA gene. Two 8 aa sequences, GHVDHGKT in IF2 and EF-Tu and DTPGHVDF in EF-G, were the longest invariant amino acid sequences detected. These sequences could be essential elements from the genome of the last common ancestor and may have remained unchanged throughout evolution. 相似文献
102.
Eleanor May Rusack Joe Dortch Ken Hayward Michael Renton Mathias Boer Pauline Grierson 《Human ecology: an interdisciplinary journal》2011,39(5):673-682
We examine the role that habitus, an individual’s or group’s dispositions, has played in the retention of traditional ecological knowledge among the Noongar
people of south-western Australia. We sought to determine if current plant knowledge reflects Noongar habitus or, alternatively, the use of fall-back species that were important due to the intermittency of agricultural employment and
the social exclusion of Aboriginal people up until at least the 1960s in Western Australia. We compared the seasonal availability
of Noongar food plant resources currently known by Noongar Elders to those described at the time of European settlement. We
used non-metric Multidimensional Scaling (nMDS) and multivariate statistics to compare the seasonal availability of plant
resources with the seasonal availability of work prior to the introduction of civil rights for Aboriginal Australians in the
1960s. We show that the seasonal pattern of plant knowledge has changed little since settlement and that there was no significant
relationship between the seasonal availability of work and plant knowledge. This result suggests that prior to 1960 Noongars
maintained a reasonably traditional round of seasonal activities involving traditional plant use. We suggest that Noongar
habitus guided their response to the colonising culture and helped preserve traditional ecological knowledge. 相似文献
103.
Masako Kitajima Yoshiko Ohkura Takayoshi Shotake Ken Nozawa 《Primates; journal of primatology》1975,16(4):399-404
Genetic variation at the locus controlling A1 band of erythrocyte esterase was found in the Japanese macaque,Macaca fuscata. Existence of four alleles,Es-A 1 1 ,Es-A 1 2 ,Es-A 1 3 , andEs-A 1 4 , controlling the mobility of the band and codominance relation between them were postulated. A majority of the troops examined were monomorphic inEs-A 1 1-1 phenotype, and the variant phenotypes were observed to occur only in Yugawara-Ihama, Arashiyama, and Koshima areas. 相似文献
104.
105.
Hiroki Takagi Shintaro Sugawara Tomoka Saito Haruka Tasaki Lu Yuanxue Guan Kaiyun Dong-Sheng Han Toshinari Godo Masaru Nakano 《Plant biotechnology reports》2011,5(2):187-195
The gesneriaceous perennial plant Titanotrichum oldhamii has beautiful foliage and attractive bright yellow flowers. However, breeding of T. oldhamii by conventional sexual hybridization may be difficult because sexual reproduction of this species is very rare. In the present
study, plant regeneration systems via both direct and indirect formation of adventitious shoots from leaf explants were established
as the first step toward breeding T. oldhamii by using biotechnological techniques. Adventitious shoots were formed efficiently on medium containing 0.1 mg l−1 benzyladenine. Histological observation showed that shoot formation on this medium occurred directly from leaf epidermal
cells without callus formation. On the other hand, leaf explants formed calluses on medium containing 0.1 mg l−1 2,4-dichlorophenoxyacetic acid. The calluses could be maintained by monthly subculturing to fresh medium of the same composition.
When the calluses were transferred to plant growth regulator-free medium, they formed adventitious shoots. Directly and indirectly
formed shoots rooted well on medium containing 0.1 mg l−1 indole-3-butyric acid. Plantlets thus obtained were successfully acclimatized and grew vigorously in the greenhouse. Flow
cytometry analysis indicated that no variation in the ploidy level was observed in plants regenerated via direct shoot formation,
whereas chromosome doubling occurred in several plants regenerated via indirect shoot formation. Regenerated plants with the
same ploidy level as the mother plants showed almost the same phenotype as the mother plants, whereas chromosome-doubled plants
showed apparent morphological alterations: they had small and crispate flowers, and round and deep green leaves. 相似文献
106.
Cloning and functional expression of ATA1, a subtype of amino acid transporter A, from human placenta 总被引:7,自引:0,他引:7
Wang H Huang W Sugawara M Devoe LD Leibach FH Prasad PD Ganapathy V 《Biochemical and biophysical research communications》2000,273(3):1175-1179
This report describes the primary structure and functional characteristics of human ATA1, a subtype of the amino acid transport system A. The human ATA1 cDNA was isolated from a placental cDNA library. The cDNA codes for a protein of 487 amino acids with 11 putative transmembrane domains. The transporter mRNA ( approximately 9.0 kb) is expressed most prominently in the placenta and heart, but detectable level of expression is evident in other tissues including the brain. When expressed heterologously in mammalian cells, the cloned transporter mediates Na(+)-coupled transport of the system A-specific model substrate alpha-(methylamino)isobutyric acid. The transport process is saturable with a Michaelis-Menten constant of 0. 89 +/- 0.12 mM. The Na(+):amino acid stoichiometry is 1:1 as deduced from the Na(+)-activation kinetics. The transporter is specific for small short-chain neutral amino acids. The gene for the transporter is located on human chromosome 12. 相似文献
107.
Yanwen Jiang David Redmond Kui Nie Ken W Eng Thomas Clozel Peter Martin Leonard HC Tan Ari M Melnick Wayne Tam Olivier Elemento 《Genome biology》2014,15(8)
Background
Molecular mechanisms associated with frequent relapse of diffuse large B-cell lymphoma (DLBCL) are poorly defined. It is especially unclear how primary tumor clonal heterogeneity contributes to relapse. Here, we explore unique features of B-cell lymphomas - VDJ recombination and somatic hypermutation - to address this question.Results
We performed high-throughput sequencing of rearranged VDJ junctions in 14 pairs of matched diagnosis-relapse tumors, among which 7 pairs were further characterized by exome sequencing. We identify two distinctive modes of clonal evolution of DLBCL relapse: an early-divergent mode in which clonally related diagnosis and relapse tumors diverged early and developed in parallel; and a late-divergent mode in which relapse tumors developed directly from diagnosis tumors with minor divergence. By examining mutation patterns in the context of phylogenetic information provided by VDJ junctions, we identified mutations in epigenetic modifiers such as KMT2D as potential early driving events in lymphomagenesis and immune escape alterations as relapse-associated events.Conclusions
Altogether, our study for the first time provides important evidence that DLBCL relapse may result from multiple, distinct tumor evolutionary mechanisms, providing rationale for therapies for each mechanism. Moreover, this study highlights the urgent need to understand the driving roles of epigenetic modifier mutations in lymphomagenesis, and immune surveillance factor genetic lesions in relapse.Electronic supplementary material
The online version of this article (doi:10.1186/s13059-014-0432-0) contains supplementary material, which is available to authorized users. 相似文献108.
The effects of numerous ionophores and inhibitors were tested on methane synthesis, intracellular ATP and potassium concentrations, and the proton motive force of the methanogenic archaebacterium Methanobacterium bryantii. M. bryantii had an internal pH near 6.8 (and hence little ΔpH during growth) with an electrical potential of ?127 mV in growth medium and ?105 mV in a pH 6.5 buffer. The study has identified agents which, in M. bryantii, can effectively cause a decline of intracellular ATP (gramicidin, acetylene) and potassium concentrations (gramicidin, nigericin), inhibit methane synthesis (acetylene, gramicidin, nigericin, triphenylmethylphosphonium bromide), eliminate the electrical potential (high extracellular potassium ion concentrations), and dissipate artificially imposed, inside alkaline, pH gradients (monensin, nigericin, carbonyl cyanide m-chlorophenylhydrazone). Carbonyl cyanide m-chlorophenylhydrazone was generally ineffective in media or buffers reduced with cysteine-sulfide but could be effective in cysteine-free solutions reduced with hydrogen sulfide. 相似文献
109.
Donor–Acceptor–Acceptor's Molecules for Vacuum‐Deposited Organic Photovoltaics with Efficiency Exceeding 9% 下载免费PDF全文
Xiaozhou Che Chin‐Lung Chung Chou‐Chun Hsu Feng Liu Ken‐Tsung Wong Stephen R. Forrest 《Liver Transplantation》2018,8(19)
Three vacuum‐deposited donor–acceptor–acceptor (d–a–a') small molecule donors are studied with different side chains attached to an asymmetric heterotetracene donor block for use in high efficiency organic photovoltaics (OPVs). The donor with an isobutyl side chain yields the highest crystal packing density compared to molecules with 2‐ethylhexyl or n‐butyl chains, leading to the largest absorption coefficient and short circuit current in an OPV. It also exhibits a higher fill factor, consistent with its preferred out‐of‐plane molecular π–π stacking arrangement that facilitates charge transport in the direction perpendicular to the substrate. A power conversion efficiency of 9.3 ± 0.5% is achieved under 1 sun intensity, AM 1.5 G simulated solar illumination, which is significantly higher than 7.5 ± 0.4% of the other two molecules. These results indicate that side chain modification of d–a–a' small molecules offers an effective approach to control the crystal packing configuration, thereby improving the device performance. 相似文献
110.
Effect of Lorcaserin Alone and in Combination with Phentermine on Food Cravings After 12‐Week Treatment: A Randomized Substudy 下载免费PDF全文