全文获取类型
收费全文 | 38686篇 |
免费 | 2495篇 |
国内免费 | 15篇 |
专业分类
41196篇 |
出版年
2023年 | 226篇 |
2022年 | 526篇 |
2021年 | 919篇 |
2020年 | 524篇 |
2019年 | 681篇 |
2018年 | 948篇 |
2017年 | 792篇 |
2016年 | 1333篇 |
2015年 | 2014篇 |
2014年 | 2148篇 |
2013年 | 2941篇 |
2012年 | 3368篇 |
2011年 | 3216篇 |
2010年 | 1964篇 |
2009年 | 1692篇 |
2008年 | 2403篇 |
2007年 | 2330篇 |
2006年 | 2077篇 |
2005年 | 1862篇 |
2004年 | 1749篇 |
2003年 | 1682篇 |
2002年 | 1517篇 |
2001年 | 306篇 |
2000年 | 209篇 |
1999年 | 299篇 |
1998年 | 380篇 |
1997年 | 255篇 |
1996年 | 252篇 |
1995年 | 231篇 |
1994年 | 224篇 |
1993年 | 219篇 |
1992年 | 135篇 |
1991年 | 147篇 |
1990年 | 152篇 |
1989年 | 112篇 |
1988年 | 101篇 |
1987年 | 90篇 |
1986年 | 70篇 |
1985年 | 96篇 |
1984年 | 95篇 |
1983年 | 71篇 |
1982年 | 83篇 |
1981年 | 81篇 |
1980年 | 81篇 |
1979年 | 74篇 |
1978年 | 40篇 |
1977年 | 52篇 |
1976年 | 36篇 |
1975年 | 40篇 |
1973年 | 43篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
131.
Ettore Benedetti Benedetto Di Blasio Vincenzo Pavone Carlo Pedone Claudio Toniolo Gian Maria Bonora 《International journal of biological macromolecules》1980,2(4):217-224
The X-ray diffraction and i.r. absorption conformational analysis of has showed the absence of intramolecularly hydrogen-bonded peptide conformations in the solid state. The molecules are held together in rows of ‘cyclic dimer’ motifs through intermolecular NH … OC (acid) and OH … OC {urethane} hydrogen bonds, the secondary amide-like group of the urethane moiety being in the unusual cis conformation, whereas the carboxylic acid group in the common syn conformation. The two molecules in the unit cell present a centrosymmetric set of ?, ψ1, and ψ2 values. In polar solvents solvated species largely predominate. In saturated hydrocarbon solution non-associated and associated (mostly involving the carboxylic acid CO as the proton acceptor) species simultaneously occur. The extent of association decreases with dilution. The amount of intramolecularly hydrogen-bonded oxy-C7 and C5 forms if any, should be extremely small. The type of association at saturation seems to differ from that found in the crystalline compound obtained by precipitation with saturated aliphatic hydrocarbons (from a diethyl ether solution). 相似文献
132.
Odile Gateau Maria Rocha de Morillo Pierre Louisot Renée Morelis 《生物化学与生物物理学报:生物膜》1980,595(1):157-160
A sialyl transferase activity is found in purified mitochondria. It is not due to residual contamination and this enzymatic system is located in the outer mitochondrial membrane. This proves mitochondrial autonomy in regard to glycoconjugate sialylation. 相似文献
133.
Achiléa Lisboa Bittencourt Maria das Graças Santana Araujo Maria do Socorro Fontoura Paes 《Mycopathologia》1980,71(3):155-158
A case of a two-year-old boy with multiple subcutaneous lesions caused by Basidiobolus haptosporus is presented.The child had also a non-toxic familial goiter and clinical and radiological features of a pulmonary illness. The pulmonary manifestations only disappeared with the treatment with potassium iodide. The authors think that the pulmonary lesions must have arisen by direct spread of the fungus from the subcutaneous lesions of the chest. 相似文献
134.
Mauricio Goihman-Yahr Leo Pine Maria Cecilia Albornoz Luis Yarzabal Maria Helena De Gomez Blanca San Martin Ana Ocanto Tulio Molina Jacinto Convit 《Mycopathologia》1980,71(2):73-83
Mild sonication was used to obtain single cell suspensions of Paracoccidioides brasiliensis. These cells were intact by microscopic criteria. Direct cell counts in a given inoculum and colony formation on various media were used to determine plating efficiency. Sonicated and nonsonicated cell suspensions were used to study plating efficiency and to estimate viability by means of vital dyes. Methylene blue, Erythrosin B, and Janus green were unreliable when used with P. brasiliensis, but vital dyes were accurate when tested with Candida albicans.Acridine orange gave more meaningful results of viability. Estimates of viability, however, changed significantly as a result of relatively minor alterations in the composition of the suspending medium.In initial experiments, the plating efficiency of P. brasiliensis was dismally low. It descended abruptly with increasing dilution of inoculum. Efficiency was much improved if horse serum was added to brain heart infusion plates or if glucose glycine yeast extract (GGY) plates were incubated at room temperature and mycelial colonies were counted. With the technique we report, current plating efficiency of sonicated suspensions is of the order of 25 %. Our results and procedures have an important bearing upon those studies concerned with in vitro killing of P. brasiliensis in suspensions or with isolating this fungus from clinical or environmental specimens. 相似文献
135.
Summary Using light microscopic autoradiography it was found that in the middle S and G2 phases of the cell cycle in antheridial filaments (S + G2 + M type) ofChara vulgaris L., an intensified RNA synthesis took place. The process was correlated with enhanced binding of3H actinomycin D to the DNA template, increased RNA polymerase activity, and enhanced chromatin decondensation.This work was supported by the Polish Academy of Sciences within the project 09.7.3.1.4. 相似文献
136.
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
137.
Ana Maria Andia-Waltenbaugh Charlotte A. Tate Naomi Kraus Friedmann 《Molecular and cellular biochemistry》1981,36(3):177-184
Summary Previous work by this and other laboratories has shown that glucagon administration stimulates calcium uptake by subsequently
isolated hepatic mitochondria. This stimulation of hepatic mitochondrial Ca2+ uptake byin vivo administration of glucagon was further characterized in the present report. Maximal stimulation of mitochondrial Ca2+ accumulation was achieved between 6–10 min after the intravenous injection of glucagon into intact rats. Under control conditions,
Ca2+ uptake was inhibited by the presence of Mg2+ in the incubation medium. Glucagon treatment, however, appeared to obliterate the observed inhibition by Mg2+ of mitochondrial Ca2+ uptake. Kinetic experiments revealed the usual sigmoidicity associated with initial velocity curves for mitochondrial calcium
uptake. Glucagon treatment did not alter this sigmoidal relationship. Glucagon treatment significantly increased the Vmax for Ca2+ uptake from 292±22 to 377±34 nmoles Ca2+ /min per mg protein (n=8) but did not affect the K0.5, (6.5–8.6 μM). Since the major kinetic change in mitochondrial Ca2+ uptake evoked by glucagon is an increase in Vmax, the enhancement mechanism is likely to be an increase either in the number of active transport sites available to Ca2+ or in the rate of Ca2+ carrier movement across the mitochondrial membranes. 相似文献
138.
Pasquale Petrilli Pietro Pucci Anna Maria Garzillo Giovanni Sannia Dr. Gennaro Marino 《Molecular and cellular biochemistry》1981,35(2):121-128
Summary Reactivity of sulphydryl groups of cytosolic and mitochondrial aspartate aminotransferases from ox heart has been studied.
A total of 5 and 7 cysteine residues per monomer are present in cAATo and mAATo, respectively. In native conditions only a
single sulphydryl group can be titrated by Nbs2 while the catalytic activity remains unchanged, however in the mitochondrial isozyme the reactivity depends on the functional
state of the enzyme. Reactivity toward NEM reveals the existence of a syncatalytic sulphydryl group in the cytosolic isozyme.
Titration of cAATo with pMB at pH 8 and pH 5 confirms the existence of two exposed sulphydryl groups with a different reactivity.
The results compared with those reported on the corresponding isozymes from pig and chicken heart show that syncatalytic sulphydryl
groups are of general occurrence in these enzymes. 相似文献
139.
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
140.
Erika Stix Maria L. Ferretti Ruth M. Leuschner 《Plant biology (Stuttgart, Germany)》1977,90(1):541-551
Jahreszeitliche und tageszeitliche Veränderungen des Haselpollengehalts der Luft nach Untersuchungen aus den Jahren 1967 bis 1972 an elf mitteleuropäischen Meßstellen. Vergleich mit einigen anderen europäischen Daten über den Haselpollengehalt der Luft. In Mitteleuropa kamen die meisten Haselpollen zu Beginn oder gegen Ende des Monats März vor. Stündliche Höchstwerte wurden in den Tag- und Abendstunden gemessen. Morgens kamen keine hohen Stundenwerte vor. Temperaturmessungen lassen vermuten, daß für hohe Haselpollengehalte der Luft in Norddeutschland höhere Temperaturen nötig sind als in südwestdeutschen Gebieten. 相似文献