全文获取类型
收费全文 | 63850篇 |
免费 | 17644篇 |
国内免费 | 17篇 |
专业分类
81511篇 |
出版年
2023年 | 238篇 |
2022年 | 618篇 |
2021年 | 1313篇 |
2020年 | 2643篇 |
2019年 | 4286篇 |
2018年 | 4648篇 |
2017年 | 4768篇 |
2016年 | 5289篇 |
2015年 | 5885篇 |
2014年 | 5679篇 |
2013年 | 6897篇 |
2012年 | 5081篇 |
2011年 | 4650篇 |
2010年 | 4906篇 |
2009年 | 3424篇 |
2008年 | 3044篇 |
2007年 | 2588篇 |
2006年 | 2309篇 |
2005年 | 2160篇 |
2004年 | 2022篇 |
2003年 | 1946篇 |
2002年 | 1780篇 |
2001年 | 587篇 |
2000年 | 430篇 |
1999年 | 455篇 |
1998年 | 399篇 |
1997年 | 263篇 |
1996年 | 269篇 |
1995年 | 247篇 |
1994年 | 241篇 |
1993年 | 230篇 |
1992年 | 160篇 |
1991年 | 171篇 |
1990年 | 177篇 |
1989年 | 121篇 |
1988年 | 114篇 |
1987年 | 107篇 |
1986年 | 84篇 |
1985年 | 108篇 |
1984年 | 101篇 |
1983年 | 81篇 |
1982年 | 91篇 |
1981年 | 84篇 |
1980年 | 87篇 |
1979年 | 84篇 |
1978年 | 45篇 |
1977年 | 58篇 |
1975年 | 51篇 |
1973年 | 53篇 |
1972年 | 43篇 |
排序方式: 共有10000条查询结果,搜索用时 16 毫秒
71.
Summary A 2-year-old girl had a de novo duplication in the long arm of one chromosome 7 and an increased level of the enzyme -glucuronidase in cultured fibroblasts. The phenotype of the girl partly overlaps those of two presumptive syndromes due to secondary partial trisomies 7q. The ratio of the enzyme activity was 1.43 to the controls, and 1.37 to her parent's values. We could not define the abnormality but suggest two alternatives: either the patient is trisomic for region q112 to q22 or for the region q22 to q34. If the second alternative is correct the locus for -glucuronidase is possibly assigned to band 7q22. 相似文献
72.
Maria Cobianu-Bacanu 《Dialectical Anthropology》1977,2(1):301-308
Conclusion These American anthropological studies both reflect and distort our own Romanian-conceptions. Paradoxically, this gives both Romanian and American researchers an opportunity to verify their validity and reliability. The studies are notable for their multiplicity of theoretical approaches to Romanian reality: each author brings in something new by way of interpretation and, at the same time, maintains a dialectical conception as a methodological frame of reference.The authors are certainly conversant with present and future strategies of development in Romania. But their main problem is that they do not always understand the spirit of the latter and consequently fail to interpret contemporary Romanian realities in a deeply humanistic way.And now, some proposals. For a more active dialogue between Romanian and American scientists I suggest a more comprehensive use of the Romanian sources of information, including historical, beletristic, sociological, and political works. With reference to their reflections on history, the American anthropologists could have discussions with Romanian historians, and could use Romanian historical periodization, especially for the contemporary period. For us, the following sequence is basic: the moment of the armed insurrection as the beginning of the popular democratic revolution (August 23, 1944); proclamation of a Peoples' Republic of Romania (December 30, 1947); unification of Social Democratic Party with the Communist Party to form the Romanian Workers Party (Spring 1948); at this time it is possible to speak of a socialist revolution. The analysis of the Americans should take into consideration these important dates in Romanian history and structure their studies accordingly. Sometimes they must pay more attention to the affective connotation of words, especially for a Romanian reader. Such words would be, for example, their use of elite, rather than leaders, bureaucracy rather than administration, pressure rather than social necessities with the consciousness of development, patronclient instead of using interpersonal relations with mutual benefit, etc.I would also urge that substantive discussions between Romanians and Americans begin, built around specific topics of mutual interest, rather than ceremonial meetings which occur when the parties have neither the language skills, data nor social conceptions to interact fruitfully.I suggest to the American researchers that they maintain and strengthen their contacts with Romanian administrators at local, regional and national levels, so that their studies may contribute to our social praxis.Finally, the Americans should always take into account the economic constraints that shape political, juridical, moral, and philosophical phenomena, and try also to grasp more fully the interaction between elements of the superstructure and between superstructure and base in contemporary Romanian socialist society.Above all, along with Professor Cole , I hope that the scientific effort at interpreting Romanian reality, with its lights and shadows, will be used only for reciprocal knowledge and cooperation.Maria Cobianu-Bacanu is Scientific Researcher at the Center for Sociology, Academy of Social and Political Sciences, Bucharest, Romania.
相似文献
相似文献
73.
74.
Chlorine concentrations below 0.8 mg/liter inactivated poliovirus without causing separation of the viral components. These results indicate that the release of RNA from the capsids is the result, not the cause, of virus inactivation by chlorine. 相似文献
75.
A new method is proposed for the microtitration of CBPP vaccines by performing eight parallel endpoint two-fold dilutions. When performed on a 96-well plate, it gives a titre with a precision of +/- 0.2 log10. By comparison, the established method, performed in tubes, gives a precision of only +/- 0.6 log10. The adaptation to microtitre plates allows much more economical culture of larger numbers of samples. Statistical analysis permits determination of vial-to-vial homogeneity of a batch and calculation of a titre with a precision of +/- 0.09 log10. The new method may be applied for the titration of mycoplasmas. 相似文献
76.
Dr. Laura Curatolo Christine Chaponnier Maria Benedetta Donati Luciano Morasca Giulio Gabbiani 《Cell and tissue research》1982,223(3):665-673
Summary It is known that human and animal fibroblasts are able to induce the retraction of a fibrin clot. In the present study the correlation between (i) fibrinclot retractile (FCR) activity, (ii) the number of actin stress-lines in mouse fibroblasts during growth in culture, and (iii) the sensitivity of actin stress-lines to a powerful actin-depolymerizing factor (ADF), present in plasma and serum of humans and laboratory animals was investigated. Fibroblasts at early passages (2–4) were tested for these parameters at various intervals after seeding (24, 96, and 168 h). The number of actin stress-lines was progressively higher, while the sensitivity to ADF action was progressively lower in cells cultured from 24 to 168 h; the FCR capacity was significantly decreased at 168 h. These data suggest that cells containing weakly polymerized and/or stabilized actin are more active than those containing highly polymerized and/or stabilized actin in triggering fibroblast contraction. 相似文献
77.
Age-dependent population diffusion with external constraint 总被引:3,自引:0,他引:3
We present a simple model for age dependent population diffusion when the dynamics is submitted to external constraints. Existence, uniqueness and dependence on the parameters of the solution are discussed.This work has been done within the framework of the cultural agreement between the Universities of Bordeaux and Rome 相似文献
78.
Howard R. Morris Maria Panico Michael Barber Robert S. Bordoli Robert D. Sedgwick Andrew Tyler 《Biochemical and biophysical research communications》1981,101(2):623-631
We have studied a selection of peptides using a new mass spectrometric ionisation technique - fast atom bombardment (FAB). We define the fragmentation pathways observed and comment on the utility in sequence analysis. A simple acetylation experiment is shown to aid rapid sequence assignment. 相似文献
79.
We have fractionated human peripheral blood lymphocytes (PBL) into subclasses with an affinity technique that takes advantage of the specific interaction between the plant lectin, Lens culinaris agglutinin (Lentil-PHA), and its cell surface receptors. PBL were incubated in plastic tubes or petri dishes coated with a gelatin layer to which lentil-PHA had been coupled using a water soluble carbodiimide compound. Adherent cells were recovered by melting the gelatin, and bound lectin was removed by exposing the cells to an appropriate sugar hapten. Approximately 25 to 50% of PBL specifically adhered to gelatin-coated tubes derivatized with lentil-PHA. Binding studies with 125I-labeled lentil-PHA showed that, compared to unfractionated PBL which bound 2.0 × 106 lentil-PHA molecules per cell, adherent cells bound more (3.7 × 106/cell), and nonadherent cells bound less (1.1 × 106/cell) lentil-PHA. By contrast, there were no differences among these groups for binding of other plant lectins. When stimulated in vitro by optimal mitogenic concentrations of lentil-PHA, lymphocytes adherent to lentil-PHA responded better than their nonadherent counterparts whereas the two groups responded the same to stimulation by the leukoagglutinin from Ph. vulgaris. The data indicate that plant lectins may be used to isolate PBL subclasses with different structural and functional properties. 相似文献
80.
Maria L. Bade Alfred Stinson 《Biochemical and biophysical research communications》1978,84(2):381-388
During the molt, chitin in the old cuticle of is digested by chitinase taken up from molting fluid, but the chitin in intact (= premolt) cuticle is not accessible to chitinase. As a prerequisite of digestion, old cuticle chitin is rendered competent to serve as chitinase substrate in a reaction attributable to trypsin-like proteolytic activity of molting fluid. 相似文献