全文获取类型
收费全文 | 2810篇 |
免费 | 230篇 |
国内免费 | 4篇 |
出版年
2023年 | 20篇 |
2022年 | 43篇 |
2021年 | 103篇 |
2020年 | 49篇 |
2019年 | 65篇 |
2018年 | 77篇 |
2017年 | 54篇 |
2016年 | 90篇 |
2015年 | 171篇 |
2014年 | 193篇 |
2013年 | 217篇 |
2012年 | 218篇 |
2011年 | 228篇 |
2010年 | 150篇 |
2009年 | 116篇 |
2008年 | 165篇 |
2007年 | 163篇 |
2006年 | 142篇 |
2005年 | 136篇 |
2004年 | 134篇 |
2003年 | 114篇 |
2002年 | 81篇 |
2001年 | 19篇 |
2000年 | 12篇 |
1999年 | 17篇 |
1998年 | 26篇 |
1997年 | 18篇 |
1996年 | 9篇 |
1995年 | 18篇 |
1994年 | 21篇 |
1993年 | 22篇 |
1992年 | 12篇 |
1991年 | 12篇 |
1990年 | 9篇 |
1989年 | 9篇 |
1988年 | 4篇 |
1987年 | 8篇 |
1985年 | 11篇 |
1984年 | 7篇 |
1983年 | 8篇 |
1982年 | 11篇 |
1981年 | 5篇 |
1980年 | 7篇 |
1979年 | 5篇 |
1978年 | 8篇 |
1977年 | 5篇 |
1976年 | 7篇 |
1975年 | 6篇 |
1974年 | 5篇 |
1973年 | 4篇 |
排序方式: 共有3044条查询结果,搜索用时 46 毫秒
1.
2.
Danielle E. Haulsee Dewayne A. Fox Matthew W. Breece Tonya M. Clauss Matthew J. Oliver 《PloS one》2016,11(2)
We developed a long-term tagging method that can be used to understand species assemblages and social groupings associated with large marine fishes such as the Sand Tiger shark Carcharias taurus. We deployed internally implanted archival VEMCO Mobile Transceivers (VMTs; VEMCO Ltd. Nova Scotia, Canada) in 20 adult Sand Tigers, of which two tags were successfully recovered (10%). The recovered VMTs recorded 29,646 and 44,210 detections of telemetered animals respectively. To our knowledge, this is the first study to demonstrate a method for long-term (~ 1 year) archival acoustic transceiver tag implantation, retention, and recovery in a highly migratory marine fish. Results show low presumed mortality (n = 1, 5%), high VMT retention, and that non-lethal recovery after almost a year at liberty can be achieved for archival acoustic transceivers. This method can be applied to study the social interactions and behavioral ecology of large marine fishes. 相似文献
3.
4.
5.
6.
7.
Danielle L. Laval-Martin Isabelle A. Carr Saverio J. Barbera Leland N. Edmunds 《Chronobiology international》1990,7(2):99-105
-We have previously shown that NAD kinase and NADP phosphatase activities display circadian rhythms, in the soluble (SN) and membrane-bound (P) fractions of crude extracts of the achlorophyllous ZC mutant of the phytoflagellate Euglena gracilis (which displays circadian rhythmicity of cell division). We determined if changes in the affinity of NADP phosphatase and NAD kinase for their substrates, NADP+ and NAD+, were occurring by calculating the ratios 100(velocity found in Km conditions/velocity found in saturating conditions). The rationale was that if the affinity remained unchanged according to circadian time (CI), these values should always equal 50, independently of any changes in enzyme quantity; values greater than 50 should indicate increases in enzyme affinity, and values less than 50 decreases in affinity. Our results indicated that these values calculated for NADP phosphatase exhibited a complex pattern of rhythmicity, while those for NAD kinase displayed circadian variations strongly correlated with the rhythms in enzyme activity. The curves showed troughs at CT 00-04 both in dividing and nondividing cells and peaks at CT 18-20 or at CT 08-14 in cells sampled, respectively, from a dividing or a stationary culture. Such variations are indicative of changes in the kinetic properties of the enzyme, which may reflect modifications in its affinity either for effectors (such as Ca2+-calmodulin) or for its substrate, NAD+. This may be due to (i) the expression of different isoenzymes at different CTs; (ii) different posttranslational modifications of the enzyme; or (iii) concentrations of effectors varying in a circadian manner. 相似文献
8.
A simple procedure is described for the determination of the photosensitizing potency of drugs, using three leukemic cell lines, two of lymphocytic origin, L1210 and P388 and one of erythroid type, Friend-745. The procedure allows one to investigate several aspects of the photosensitization properties of tested compounds such as cellular localization and direct (trypan blue exclusion) or delayed (clonogenicity) photomediated toxicities.The method was assessed using crude hematoporphyrin derivative (HPD) as well as dihematoporphyrin ether (DHE) or commercially available Photofrin II. Results were compared to those obtained with normal cells, e.g spleen lymphocytes and erythropoietic stem cells (CFU-e), and discussed in the light of the relative response of normal versus transformed cells.Abbreviations DHE
Dihematoporphyrin Ether
- FCS
Fetal Calf Serum
- HPD
Hematoporphyrin Derivative
- PDT
Photodynamic Therapy 相似文献
9.
Apical cuttings of Solanum tuberosum L. cv. Sirtema were used al different stages of development to study long-distance transport of phosphate. The effects of two hormones, gibberellic acid (GA3 ) and abscisic acid (ABA), on this process were also investigated. Before tuberization, phosphate (32 P) supplied to a single leaf was transported preferentially in the young and growing parts of the plant: apical bud, young leaves and roots. After tuberization, the tuber became the principal site of phosphate accumulation. GA3 treatment (10−4 M) of the tuber as well as of the leaves led to reduced transport of 32 P into the tuber. By contrast, treatment of the tuber with ABA (10−4 M) did not change the 32 P distribution within the plant, while foliar spray with ABA greatly increased the transport into the tuber. The opposite effects of the two hormones on phosphate accumulation by tubers are discussed with regard to their opposite effects on the tuberization process. 相似文献
10.
Ralph J. Graff Michael E. Kurtz Robert Paul Danielle Martin Derry C. Roopenian 《Immunogenetics》1991,33(2):96-100
The purpose of this work was to elucidate the genetic fine structure of the central portion of mouse chromosome (Chr) 2. Seven Chr 2 congenic mouse strains [B10.PA(L)-pa we un a
t
, B10.PA(L)-pa A
w
, B10.PA(L)-we un a
t
, B10.PA(J)-pa a, B10.FS-we A
w
, B10.C-we A
w
, and B10.YBR-a] were produced. Breeding studies were carried out using strains B10.PA(L)-pa we un a
t
and B10.LP-H-13
b
to accurately determine the recombination frequencies between marker genes pa and we (1.9%±0.3), we and un (8.8%±0.5), and un and a
t
(4.5%±0.4) of strain B10.PA(L)-pa we un a
t
. These strains and other Chr 2 congenic strains were typed for immunologically defined loci using monoclonal antibody (mAb) C23 reactive with the gene product of B2m
b
T-lymphocyte clone C1 reactive with the gene product of H-3
a
and H-3
c
, and lymphocyte clone H1.8 reactive with the gene product of Hd-1
a
. B2m and H-3 typing located a recombinational event separating [pa B2m H-3] from we (the order of bracketed genes is not known). Hd-1 typing indicated that Hd-1 maps distal to [H-42, H-44] and proximal to un. The gene order [pa, B2m, H-3], we, [H-42, H-45], Hd-1, un, H-13, a
t
, with H-44 mapping centromeric to Hd-1, is indicated by the data.
Address correspondence and offprint requests to: R. J. Graff. 相似文献