全文获取类型
收费全文 | 1068450篇 |
免费 | 116925篇 |
国内免费 | 1035篇 |
专业分类
1186410篇 |
出版年
2018年 | 9469篇 |
2016年 | 12766篇 |
2015年 | 17653篇 |
2014年 | 20776篇 |
2013年 | 29514篇 |
2012年 | 33159篇 |
2011年 | 34193篇 |
2010年 | 23251篇 |
2009年 | 21311篇 |
2008年 | 30575篇 |
2007年 | 31956篇 |
2006年 | 30075篇 |
2005年 | 28608篇 |
2004年 | 28766篇 |
2003年 | 27390篇 |
2002年 | 26706篇 |
2001年 | 41928篇 |
2000年 | 42114篇 |
1999年 | 33886篇 |
1998年 | 12993篇 |
1997年 | 13327篇 |
1996年 | 12575篇 |
1995年 | 11966篇 |
1994年 | 11531篇 |
1993年 | 11708篇 |
1992年 | 29187篇 |
1991年 | 28759篇 |
1990年 | 28347篇 |
1989年 | 27686篇 |
1988年 | 26167篇 |
1987年 | 24777篇 |
1986年 | 23313篇 |
1985年 | 23570篇 |
1984年 | 19770篇 |
1983年 | 17070篇 |
1982年 | 13320篇 |
1981年 | 12032篇 |
1980年 | 11424篇 |
1979年 | 18926篇 |
1978年 | 15140篇 |
1977年 | 13934篇 |
1976年 | 13257篇 |
1975年 | 14658篇 |
1974年 | 16170篇 |
1973年 | 15879篇 |
1972年 | 14560篇 |
1971年 | 13361篇 |
1970年 | 11592篇 |
1969年 | 11474篇 |
1968年 | 10750篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
991.
M N Diachina L T Sukhenko A A Iushchenko G A Ermolin 《Zhurnal mikrobiologii, epidemiologii, i immunobiologii》1985,(1):64-68
Diagnostic test systems for the detection of IgG and IgM to Mycobacterium leprae in the blood sera of leprosy patients and armadillos experimentally infected with M. leprae have been developed on the basis of the indirect immunoperoxidase assay. The possibility has been shown of prognosing the activity of the leprotic process in leprosy patients and the results of the experimental infection of armadillos by the dynamic increase of antibody reactions with the development of the infection. 相似文献
992.
J. A. Roubos C. D. de Gooijer G. van Straten A. J. B. van Boxtel 《Bioprocess and biosystems engineering》1997,17(2):99-102
Two methods for the calculation of optimal trajectories for the input variables of a fed-batch culture of hybridoma cells are compared. It pointed out that a gradient method based on Pontryagins' minimum principle based yields a significant better performance with respect to computational effort and the calculated minimum than a dynamic programming approach which has been presented in a previous paper [1] as the most suitable method. 相似文献
993.
Crystallization and preliminary crystallographic studies of the decadeoxyoligonucleotide d(CpGpTpApCpGpTpApCpG) 总被引:1,自引:0,他引:1
Crystals of the self-complementary decadeoxyoligonucleotide d(CpGpTpApCpGpTpApCpG) have been grown from a solution containing [Co(NH3)6]Cl3 and spermine. The amber-colored crystals are hexagonal and belong to the space group P6(5) (or P6(1] with unit cell parameters a = 17.93 A, c = 43.41 A. Precession photography and molecular packing considerations indicate that the unit cell consists of a 12 nucleotide duplex. The asymmetric unit, therefore, is a disordered duplex dimer in which each pyrimidine-purine base-pair is occupied 60% of the time by a C . G pair and 40% of the time by a T . A pair. The above considerations and preliminary structure analysis reveal that this alternating pyrimidine-purine oligomer assumes a Z-DNA conformation. 相似文献
994.
995.
996.
A P Khokhlov K N Iarygin A G Shitin 《Biulleten' eksperimental'no? biologii i meditsiny》1986,102(8):160-162
The in vitro treatment of membranes isolated from different rat organs with a water-soluble synthetic antioxidant has resulted in the change of basal and stimulus-induced adenylate cyclase activity. It is believed that the antioxidant effect is realized rather at the level of signal transfer from activated receptor to adenylate cyclase than at the level of agonist-receptor interaction. 相似文献
997.
A strain of Methylomonas albus BG8WM, a type 1 obligate methanotroph, which had been maintained for 2 ycars by serial passage on solid medium containing methanol as a carbon source was found to mutate at a frequency of 10-5-10-6 to resistance to dichloromethane (DCMR), the parental strain BG8 did not give rise to DCMR colonies. DCMR strains were no longer capable of growth on methane as a carbon cource and exhibited greatly reduced or undetectable methane mono-oxygenase activity. The mutants fell into three groups on the basis of SDS-PAGE analysis of the polypeptide profiles of the particulate fraction of cell extracts. One or more of four polypeptides of Mr 70,000, 50,000, 25,000 and 23,000 were implicated as being components of the methane mono-oxygenase. Spontaneous reversion to growth on methane and sensitivity to dichloromethane occurred at a frequency of about 10-8. The loss of methane mono-oxygenase activity was not associated with loss of the resident 55 kb plasmid.Abbreviations DCMR
dichloromethane-resistant
- SDS-PAGE
sodium dodecyl sulphate polyacrylamide gel electrophoresis
- NMS
nitrate minimal salts medium 相似文献
998.
Predator detection and avoidance by starlings under differing scenarios of predation risk 总被引:3,自引:0,他引:3
Devereux Claire L.; Whittingham Mark J.; Fernandez-Juricic Esteban; Vickery Juliet A.; Krebs John R. 《Behavioral ecology》2006,17(2):303-309
Practically all animals must find food while avoiding predators.An individual's perception of predation risk may depend on manyfactors, such as distance to refuge and group size, but it isunclear whether individuals respond to different factors ina similar manner. We tested whether flocks of foraging starlingsresponded in the same way to an increased perception of predationrisk by assessing three factors: (1) neighbor distances, (2)habitat obstruction, and (3) recent exposure to a predator.We found that in all three scenarios of increased risk, starlingsreduced their interscan intervals (food-searching bouts), whichincreased the frequency of their vigilance periods. We thenexamined how one of these factors, habitat obstruction, affectedescape speed by simulating an attack with a model predator.Starlings were slower to respond in visually obstructed habitats(long grass swards) and slower when they had their head downin obstructed habitats than when they had their head down inopen habitats. In addition, reaction times were quicker whenstarlings could employ their peripheral fields of vision. Ourresults demonstrate that different sources of increased riskcan generate similar behavioral responses within a species.The degree of visibility in the physical and social environmentaffects both the actual and perceived risk of predation. 相似文献
999.
1000.
Fixation with a saturated aqueous solution of potassium pyroantimonate produces electron-opaque antimonate deposits in the nucleoli of lutheinic and hepatic cells. The comparative analysis between normal and actinomycin D segregated nucleoli fixed either with glutaraldehyde-osmium or potassium pyroantimonate facilitates location of the ring-shaped precipitates in the fibrillar centers and the fine dense ones in the pars fibrosa. 相似文献