全文获取类型
收费全文 | 1122238篇 |
免费 | 117877篇 |
国内免费 | 434篇 |
专业分类
1240549篇 |
出版年
2018年 | 10597篇 |
2017年 | 10091篇 |
2016年 | 14541篇 |
2015年 | 19238篇 |
2014年 | 22699篇 |
2013年 | 32589篇 |
2012年 | 36658篇 |
2011年 | 37670篇 |
2010年 | 25808篇 |
2009年 | 23913篇 |
2008年 | 34074篇 |
2007年 | 35287篇 |
2006年 | 33234篇 |
2005年 | 32050篇 |
2004年 | 31816篇 |
2003年 | 30399篇 |
2002年 | 29902篇 |
2001年 | 44927篇 |
2000年 | 44304篇 |
1999年 | 36067篇 |
1998年 | 14189篇 |
1997年 | 14242篇 |
1996年 | 13473篇 |
1995年 | 12548篇 |
1994年 | 12139篇 |
1993年 | 12223篇 |
1992年 | 29824篇 |
1991年 | 29340篇 |
1990年 | 28717篇 |
1989年 | 28073篇 |
1988年 | 26098篇 |
1987年 | 25159篇 |
1986年 | 23445篇 |
1985年 | 23444篇 |
1984年 | 19750篇 |
1983年 | 17167篇 |
1982年 | 13391篇 |
1981年 | 12213篇 |
1980年 | 11410篇 |
1979年 | 18456篇 |
1978年 | 14728篇 |
1977年 | 13483篇 |
1976年 | 12957篇 |
1975年 | 14093篇 |
1974年 | 15435篇 |
1973年 | 15215篇 |
1972年 | 13873篇 |
1971年 | 12505篇 |
1970年 | 11066篇 |
1969年 | 10866篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
981.
982.
T. R. Consi E. R. Macagno 《Journal of comparative physiology. A, Neuroethology, sensory, neural, and behavioral physiology》1985,156(1):135-143
Summary The crustaceanDaphnia magna responds to a flash of light with a ventral rotation of its compound eye; this behavior is termed eye flick. We determined the spectral sensitivity for the threshold of eye flick in response to light flashes having three different spatial characteristics: (1) full-field, extending 180° from dorsal to ventral in the animal's field of view; (2) dorsal, 30° wide and located in the dorsal region of the visual field; (3) ventral, same as dorsal but located ventrally. All three stimuli extended 30° to the right and to the left of the animal's midplane. We found that spectral sensitivity varies with the spatial characteristics of the stimulus. For full-field illumination, the relative sensitivity was maximal at 527 nm and between 365 nm and 400 nm, with a significant local minimum at 420 nm. For the dorsal stimulus, the relative sensitivity was greatest at 400 nm, but also showed local maxima at 440 nm and 517 nm. For the ventral stimulus, the relative sensitivity maxima occurred at the same wavelengths as those for the full-field stimulus. At wavelengths of 570 nm and longer, the responses to both dorsal and ventral stimuli showed lower relative sensitivity than the full-field stimulus. No circadian or other periodic changes in threshold spectral sensitivity were observed under our experimental conditions. Animals which had their nauplius eyes removed by means of laser microsurgery had the same spectral sensitivity to full-field illumination as normal animals. Our results are discussed in terms of our current knowledge of the spectral classes of photoreceptors found in theDaphnia compound eye. 相似文献
983.
A Sólyom S Tóth I Holczinger J Vajda Z Tóth R Kálmánchey 《Applied neurophysiology》1985,48(1-6):222-225
Four thalamic and cortical recordings were carried out in 5 patients. The thalamic-evoked potentials were typical and revealed a triphasic complex, but their latencies showed a relatively high standard deviation. They could be divided into two groups according to their latencies, both of which had low SD. These data suggested that there could be two types of latency of thalamic SEP, because the 4 patients' body sizes were very similar. More detailed surface, cortical and depth recordings are needed to resolve these questions. 相似文献
984.
E. Bomsdorf 《Biometrical journal. Biometrische Zeitschrift》1985,27(7):753-758
The measures of dispersion for ungrouped data proposed by Gini and Lienert, which are defined as the mean of the ranges of pairs and triplets of n values, are generalised. A family of measures of dispersion emerges with weights based on ranks instead of the measurements themselves. 相似文献
985.
Isolation of serum chylomicrons prior to density gradient ultracentrifugation of other serum lipoprotein classes 总被引:1,自引:0,他引:1
A H Terpstra 《Analytical biochemistry》1985,150(1):221-227
A method for the removal of serum chylomicrons before density gradient ultracentrifugation of the other serum lipoproteins using an SW 41 swinging bucket rotor is presented. In a preliminary spin, the chylomicrons with an Sf greater than 400 X 10(-13) s float to the top of the gradient, whereas the other lipoproteins are retained in the infranatant fraction. After removal of the chylomicrons, the other serum lipoproteins are subsequently fractionated by isopycnic density gradient ultracentrifugation. Analysis of the separated lipoprotein fractions suggested that this procedure permits isolation of a chylomicron fraction consisting solely of chylomicrons but that the very low density lipoprotein fraction subsequently isolated also contains chylomicrons or chylomicron remnants with an Sf less than 400 X 10(-13) s, and that there is considerable overlap in flotation rate and particle size of very low density lipoproteins and chylomicrons. 相似文献
986.
S. Goldenberg J.M. Salles V.T. Contreras M.P.Lima Franco A.M. Katzin W. Colli C.M. Morel 《FEBS letters》1985,180(2):265-270
The cell-free translation products of polyribosomal and post-polyribosomal mRNAs from the non-infective epimastigotes and the infective metacyclic trypomastigotes of the parasitic protozoan Trypanosoma cruzi were compared by two-dimensional polyacrylamide gel electrophoresis. The result show that although many polypeptides are conserved, quantitative and qualitative differences are observed between both differentiation stages. The results also indicate the existence of post-polyribosomal mRNAs in equilibrium with polyribosomal counterparts. The immunoprecipitation of the in vitro synthesized polypeptides with chagasic human serum and the serum raised against an 85-kDa glycoprotein (P2-WGA), potentially involved in the process of T. cruzi penetration into mammalian cells, shows that while the chagasic serum recognizes the same 72-kDa, 68-kDa and 46-kDa polypeptides in both differentiation stages, the anti-P2-WGA serum immunoprecipitates a single 48-kDa polypeptide from in vitro translation products of metacyclic trypomastigotes. 相似文献
987.
A Rhalem K Bekhti C Bourdieu G Luffau P Péry 《Comptes rendus de l'Académie des sciences. Série III, Sciences de la vie》1989,309(1):19-23
Proteins are released from the surface of sporozoites of Eimeria falciformis during their in vitro incubation in a detergent solution. Some of these proteins reacted with antibodies from infected mice and specifically stimulated the proliferation of mesenteric lymph node cells of these mice. Oral immunization of mice with liposome encapsulated sporozoite surface antigens protected mice against a challenge infection. Two proteins (M.W. 27 and 180 K) induced an antibody synthesis in these vaccinated mice. 相似文献
988.
A Levva G Schwartsmann L C Boeije H M Pinedo F de Waal 《Biochemical and biophysical research communications》1986,141(2):629-635
In the original HL-60 cells (HL-60-S) and an HL-60 subline (HL-60-R) respectively susceptible and resistant to induction of differentiation by retinoic acid or dimethyl sulfoxide, 5-aza-2'-deoxycytidine inhibited growth equally but induced differentiation to a greater extent in HL-60-S. Flow cytometry showed that 5-aza-2'-deoxycytidine produced in both HL-60 lines an increased proportion of cells in G2+M rather than G0/G1 as with retinoic acid. 5-aza-2'-deoxycytidine may have a differentiation-inducing effect in HL-60 provided cells have the competence to differentiate, indicating the importance of an alternate mechanism of action. 相似文献
989.
Glycosylated haemoglobin (HbA1) was measured in seven insulin-dependent diabetic patients before, during, and after a seven-day period of monitored poor control. There was considerable individual variation in the pattern and degree of change in HbA1 concentration induced by poor control and the time when it occurred. Greater increases in HbA1 were seen during the period of metabolic derangement than in the subsequent two months. More information is required before HbA1 estimations are widely used clinically to monitor control in individual diabetics. 相似文献
990.
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