全文获取类型
收费全文 | 22257篇 |
免费 | 2060篇 |
国内免费 | 977篇 |
出版年
2024年 | 82篇 |
2023年 | 596篇 |
2022年 | 848篇 |
2021年 | 1195篇 |
2020年 | 983篇 |
2019年 | 1224篇 |
2018年 | 1093篇 |
2017年 | 815篇 |
2016年 | 831篇 |
2015年 | 1041篇 |
2014年 | 1484篇 |
2013年 | 1934篇 |
2012年 | 1038篇 |
2011年 | 1198篇 |
2010年 | 884篇 |
2009年 | 1016篇 |
2008年 | 1026篇 |
2007年 | 953篇 |
2006年 | 890篇 |
2005年 | 816篇 |
2004年 | 741篇 |
2003年 | 572篇 |
2002年 | 547篇 |
2001年 | 443篇 |
2000年 | 331篇 |
1999年 | 305篇 |
1998年 | 300篇 |
1997年 | 282篇 |
1996年 | 213篇 |
1995年 | 178篇 |
1994年 | 253篇 |
1993年 | 167篇 |
1992年 | 161篇 |
1991年 | 112篇 |
1990年 | 101篇 |
1989年 | 71篇 |
1988年 | 80篇 |
1987年 | 57篇 |
1986年 | 57篇 |
1985年 | 58篇 |
1984年 | 55篇 |
1983年 | 48篇 |
1982年 | 43篇 |
1981年 | 37篇 |
1980年 | 25篇 |
1979年 | 27篇 |
1978年 | 20篇 |
1976年 | 15篇 |
1975年 | 13篇 |
1974年 | 14篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
111.
Cholinergic processes were measured in motor cortex, hippocampus, and striatum of cats in the terminal stages of GM1 gangliosidosis and compared to those of control cats. The greatest difference observed was elevation in the rate of K+-stimulated release of acetylcholine (ACh) from brain slices prepared from affected cats. The K+-stimulated release of endogenous ACh was increased by 31-43% and of newly synthesized ACh by 19-80% in brain slices from different brain regions. All regions that were examined were affected but the greatest effects occurred in cortex. The rate of synthesis of ACh was elevated in cortical and hippocampal slices. Choline acetyltransferase activity in brain regions of cats with GM1 gangliosidosis was not significantly different from that in controls, whereas high-affinity choline transport in cortical synaptosomes was elevated. Muscarinic receptor binding sites were reduced in the cortex, hippocampus, and striatum of GM1 mutant cats, whereas the apparent affinity was not altered. These results indicate that there are major alterations of cholinergic function in the brains of cats with GM1 gangliosidosis. 相似文献
112.
113.
Protoscoleces from human, camel, cattle, sheep, goat (all from Kenya) and buffalo (from India) hydatid cysts were cultured under identical conditions in vitro using the diphasic culture system of Smyth (1979b). Organisms from all sources grew and segmented in culture. Genital anlagen developed in all cultured worms but further genital differentiation occurred only in cultures of cattle (testes) and camel (testes and genital pore) material. The possible significance of these results is discussed in relation to the general epidemiology of hydatid disease and the potential infectivity of the different strains to man. 相似文献
114.
David M. Glassman 《Primates; journal of primatology》1985,26(3):315-324
Intracortical bone remodeling and cortical thickness data were collected from middiaphyseal thin sections of the humerus,
ulna and tibia for 47 specimens ofSaguinus fuscicollis. Individuals were classified into age cohorts: Young Adult, Mid-adult I, Mid-adult II and Old Adult. Correlation analyses
revealed significant relationships between age cohort and the number of osteons for the humerus and ulna, and between age
cohort and non-Haversian canals for each of the three long bone elements. Significant relationships between age cohort and
dimension of cortex size suggested an age-related pattern of cortical shifting in the ulna and older-age bone loss in the
tibia. 相似文献
115.
116.
马立克氏病毒单克隆抗体的研究 总被引:1,自引:0,他引:1
获得了4株分泌马立克氏病毒(MDV)特异性单克隆抗体(McAb)的杂交瘤细胞:4BS10对MDV所有毒株呈阳性反应;4CN8 对MDV血清1,3型毒株发生反应;2BN90和4CN24只对MDV血清1型毒株有阳性反应。3个McAb属IgG1,1个为IgG2b,均不中和MDV,免疫扩散试验也无沉淀线。对禽白血病毒(ALV)无交叉反应。 以2BN90和辣根过氧化物酶、异硫氰酸荧光素的结合物进行直接酶联免疫吸附试验和直接荧光抗体试验,均获得成功。抗体滴度前者为1/51,200,后者为1/640。对ALV无交叉反应。 相似文献
117.
Presence of theophylline and dibutyryl-cAMP—agents which cause elevation of intracellular levels of cAMP—in in vitro systems in which murine macrophages interact with virulent blood forms of Trypanosoma cruzi resulted in a marked inhibition of cell-parasite association (i.e., decreased surface binding and/or internalization). This effect was evidenced in terms of significant reductions in both the percentage of infected macrophages and the average number of trypanosomes per 100 macrophages. Pretreatment of the macrophages with these agents produced a similar inhibition whereas pretreatment of the parasites had no significant consequence on the interaction. The inhibitory effect was transient since it was no longer seen after 30 min of incubation of the treated macrophages in fresh medium. Thus, the inhibitory effect is exerted through a transient effect on the macrophage. 相似文献
118.
自然界甘蓝茎点霉(Phoma lingam)的有性世代为斑点小球腔菌Leptosphaeriamaculans通常形成于甘蓝属植株的越冬残茎上。在实验室内其有性阶段不易培养或需要较长的时间,而且形成假囊壳的百分率也很低。为了在实验室内能短期诱发大量L.maculans的假囊壳,本实验研究了该菌假囊壳生成的条件,创造了双层培养方法。自澳大利亚采集到有该菌假囊壳的芸苔(Brassica napus)残基,分离得到子囊孢子单孢后代数十株,同时用保存的已知交配型665(+)和666(-)为材料,研究了(+)(-)配对结合的环境条件。实验结果表明16℃的温度,近紫外光照射(黑光灯)和V_(?)麦杆琼脂培养基上可以产生少量的假囊壳。但是,若配合以双层培养,则在培养4周后可产生大量成熟的假囊壳。实验还确定了该菌在性细胞形成、交配、子囊形成和成熟等阶段对环境因子都有不同的要求。双层培养对假囊壳的发育有重要作用。前期菌体营养生长与后期假囊壳的成熟紧密相关。 相似文献
119.
Streptococcus mutans Ingbritt was grown in glucose-excess continuous culture to repress the glucose phosphoenolpyruvate phosphotransferase system (PTS) and allow investigation of the alternative glucose process using the non-PTS substrate, (3H) 6-deoxyglucose. After correcting for non-specific adsorption to inactivated cells, the radiolabelled glucose analogue was found to be concentrated approximately 4.3-fold intracellularly by bacteria incubated in 100 mM Tris-citrate buffer, pH 7.0. Mercaptoethanol or KCl enhanced 6-deoxyglucose uptake, enabling it to be concentrated internally by at least 8-fold, but NaCl was inhibitory to its transport. Initial uptake was antagonised by glucose but not 2-deoxyglucose. Evidence that 6-deoxyglucose transport was driven by protonmotive force (p) was obtained by inhibiting its uptake with the protonophores, 2,4-dinitrophenol, carbonylcyanide m-chlorophenylhydrazine, gramicidin and nigericin, and the electrical potential difference () dissipator, KSCN. The membrane ATPase inhibitor, N,N1-dicyclohexyl carbodiimide, also reduced 6-deoxyglucose uptake as did 100 mM lactate. In combination, these two inhibitors completely abolished 6-deoxyglucose transport. This suggests that the driving force for 6-deoxyglucose uptake is electrogenic, involving both the transmembrane pH gradient (pH) and . ATP hydrolysis, catalysed by the ATPase, and lactate excretion might be important contributors to pH.Abbreviations DNP
2,4-dinitrophenol
- CCCP
carbonylcyanide m-chlorophenylhydrazone
- DCCD
N,N1-dicyclohyxyl carbodiimide
- p
protonmotive force
- pH
transmembrane pH gradient
-
transmembrane electrical potential difference 相似文献
120.
Anatoli I. Yashin Kenneth G. Manton Eric Stallard 《Journal of mathematical biology》1986,24(2):119-140
Analyses of human mortality data classified according to cause of death frequently are based on competing risk theory. In particular, the times to death for different causes often are assumed to be independent. In this paper, a competing risk model with a weaker assumption of conditional independence of the times to death, given an assumed stochastic covariate process, is developed and applied to cause specific mortality data from the Framingham Heart Study. The results generated under this conditional independence model are compared with analogous results under the standard marginal independence model. Under the assumption that this conditional independence model is valid, the comparison suggests that the standard model overestimates by 4% the effect on life expectancy at age 30 due to the hypothetical elimination of cancer and by 7% the effect for cardiovascular/cerebrovascular disease. By age 80 the overestimates were 11% for cancer and 16% for heart disease. These results suggest the importance of avoiding the marginal independence assumption when appropriate data are available — especially when focusing on mortality at advanced ages. 相似文献