全文获取类型
收费全文 | 5628篇 |
免费 | 364篇 |
出版年
2023年 | 27篇 |
2022年 | 16篇 |
2021年 | 62篇 |
2020年 | 53篇 |
2019年 | 67篇 |
2018年 | 160篇 |
2017年 | 152篇 |
2016年 | 205篇 |
2015年 | 298篇 |
2014年 | 293篇 |
2013年 | 418篇 |
2012年 | 499篇 |
2011年 | 415篇 |
2010年 | 254篇 |
2009年 | 187篇 |
2008年 | 284篇 |
2007年 | 262篇 |
2006年 | 262篇 |
2005年 | 195篇 |
2004年 | 257篇 |
2003年 | 212篇 |
2002年 | 213篇 |
2001年 | 151篇 |
2000年 | 152篇 |
1999年 | 103篇 |
1998年 | 45篇 |
1997年 | 29篇 |
1996年 | 44篇 |
1995年 | 30篇 |
1994年 | 26篇 |
1993年 | 24篇 |
1992年 | 88篇 |
1991年 | 56篇 |
1990年 | 50篇 |
1989年 | 43篇 |
1988年 | 36篇 |
1987年 | 37篇 |
1986年 | 34篇 |
1985年 | 35篇 |
1984年 | 28篇 |
1983年 | 20篇 |
1982年 | 12篇 |
1980年 | 11篇 |
1978年 | 11篇 |
1975年 | 11篇 |
1974年 | 13篇 |
1973年 | 12篇 |
1972年 | 12篇 |
1970年 | 12篇 |
1969年 | 10篇 |
排序方式: 共有5992条查询结果,搜索用时 15 毫秒
41.
J M Fernández M F Rubio-Arroyo M Soriano-García R A Toscano M C Pérez-César 《Steroids》1985,45(2):151-157
The synthesis and molecular structure of prolame, N-(3-hydroxy-1,3,5(10)-estratrien-17 beta-yl)-3-hydroxypropylamine, is described. It was characterized by ir, nmr, mass spectrometry and chemical analysis. The crystal structure of this compound was determined by single-crystal x-ray diffraction. Prolame belongs to space group P212121. Cell dimensions are: a = 8.356(2), b = 13.343(4) and c = 16.119(4) A. Z = 4; R = 4.1%. 相似文献
42.
A method is given to predict the unitary free energies of complexation between drug-like and nucleoside-like biomolecules in a range of mixed solvent compositions. A stability maximum for the actinomycin (A)-deoxyguanosine (D) complex at 8% MeOH (v/v) in methanol/water mixtures is correctly predicted by the theory in agreement with existing experimental data. The molecular surface areas of A and D exposed to the solvent are found to diminish by 36.4 A(2) upon association. The 'microthermodynamic differential surface tension' of the solvophobic theory obtained for nucleoside-like and organic molecules in contact with MeOH/H2O can be used to predict the solvent effect free energies in other such molecular or biopolymeric associations in solution. 相似文献
43.
Independent experiments have shown that both protein folding (G. Velicelebi and J.M. Sturtevant, Biochemistry 18 (1979) 1180) and drug-biomolecule complexation (D.M. Crothers and D.I. Ratner, Biochemistry 7 (1968) 1823) in a wide range of compositions of methanol/water mixed solvents exhibit a maximum at 8% (v/v) MeOH. This hitherto unexplained phenomenon is shown to be given a priori by the 'solvophobic theory' developed earlier by Sinanoglu which had related the solvent effects including water in biochemistry to the then introduced 'molecular surface areas' and to 'microthermodynamic cavity inner surface tensions' and in a different version to interfacial microtensions between side chains and the solvent. Both analyses carried out in the present paper in detail for MeOH/water mixtures show how the denaturation or complexation free energies are predicted for the entire range of MeOH/water compositions from only data at one point. The molecular surface area changes for the conformational processes are obtained as well as the free energies in the hypothetical but theoretically important in vacuo limits with no solvent present. 相似文献
44.
Javier G. Fernández Velasco Norma L. Pucheu Oscar Romero Norma L. Kerber Raúl A. Fernández Augusto F. García 《Archives of microbiology》1985,143(2):192-195
The conditions under which an oscillatory behaviour is observed during net hydrolysis or synthesis of ATP in chromatophores of Rhodospirillum rubrum FR1 are described. In the case of ATPase the oscillations are observed at low temperature (ca. 11°C) in the dark after an initial transient behaviour. These oscillations are attenuated or disappear by the addition of an uncoupler.Oscillations are also observed during ATP synthesis. At 3°C the oscillations appear spontaneously if photophosphorylation is measured during a sufficiently long time. At 30°C the mere intercalation of a dark period also at 30°C is sufficient to trigger the oscillations in the following light period.Abbreviations Bchl
Bacteriochlorophyll
- FCCP
carbonyl cyanide p-trifluoromethoxyphenyl hydrazone
- PMS
phenazine methosulfate
- TMPD, N,N,N,N
tetramethyl-1,4-phenylenediamine
Dedicated to Prof. Dr. Gerhart Drews as a homage for his permanent example as hard worker and careful scientist and also for his remarkable human quality 相似文献
45.
A study was made on the phylogenetic relationships of species of the family Resedaceae, based on morphological features, chromosome meiotic behaviour, karyotype features, size and fertility of pollen grains, nucleotypic parameters, seed protein profiles and esterase isozyme patterns.For the comparison of the seed protein profiles among species a method was developed based on the presence or absence of the bands by means of a computer program. The dendrogram obtained by such a method is in line, to a great extent, with the clusters (sections) obtained within the family based on morphological features.Data on meiotic behaviour and on morphology, such as the type of fruit, carpel numbers and others, suggest that x=5 is the primitive basic chromosome number of this family. x1=6 and x2=7 are considered as secondary basic numbers derived from x=5 through aneuploid changes.The results support a proposed phylogenetic tree of the genera and sections of the genus Reseda represented in the European Flora.The principal phenomena that have operated in the evolution of the Resedaceae seem to be aneuploid changes, polyploidy and structural rearrangements. A trend towards DNA increase in the evolution of this group is also apparent. 相似文献
46.
Diazepam-induced feeding in rats is antagonized not only by the opiate antagonist naloxone but also intraventricular administration of specific antisera to the endogenous opioid peptides met-enkephalin or beta-endorphin. Pituitary beta-endorphin is probably not implicated in the diazepam effect since blockade with the glucocorticoid dexamethasone of the release of beta-endorphin from the anterior pituitary does not modify the diazepam-induced feeding, which is however prevented by TRH, a suggested physiological antagonist of some of the effects of opioid peptides. The possible central participation of both beta-endorphin and met-enkephalin in the ingestive behavior induced by diazepam gives further support to the postulated physiological role of endogenous opioids in appetite regulation. 相似文献
47.
A. Ma Fernández-Peralta J. J. González-Aguilera 《Plant Systematics and Evolution》1986,152(3-4):167-183
Six closely related taxa of the sect.Eusideritis of the genusSideritis (S. leucantha, S. pusilla, S. flavovirens, S. granatensis, S. biflora andS. osteoxylla) are analysed to elucidate their phylogenetic relationships and position within the sect.Eusideritis. Meiotic behaviour, karyotype features, size and fertility of pollen grains, DNA amounts and seed protein profiles are reviewed. A polyploid origin of the group (from x = 7) and the further diversification through dysploidy and chromosome repatterning is postulated.S. osteoxylla is apparently of hybrid origin. 相似文献
48.
A J Fernández M A Sierra A Méndez E Mozos M C Moyano L Carrasco 《Cell structure and function》1986,11(4):379-382
Effects of septic shock by repeated inoculations with Escherichia coli on the ultrastructure of the folliculo-stellate cells and cavities of the adenohypophysis of the chicken were investigated in order to determine the function of these cavities. The principal morphological modifications were dilation of the Golgi apparatus, endoplasmic reticulum and autophagic vacuoles, and necrosis phenomena in the stellate cells. The follicular cavities showed dilation, and there was heterogeneous dense material and granular elements in the follicular lumen. Based on results reported in the literature, the observations reported here are evidence of a "cleaning-role", for the removal of cell debris, when there is endocrine disfunction. 相似文献
49.
The influence of surfactant micelles on the acid-base dissociation of the charged tertiary amino group of the local anesthetic, tetracaine, has been investigated. From measurements of tetracaine fluorescence as a function of bulk pH, apparent values of 6.88, 7.58 and 9.92 were found in the presence of cationic, neutral and anionic micelles, respectively, in 10 mM NaCl. These values are considerably displaced with respect to the in aqueous solution which is 8.26. Such large shifts can be attributed to the effect of the surface polarity and electrical potential on the dissociation behavior of the anesthetic bound to micelles. It can be expected that the acid-base dissociation of a local anesthetic adsorbed to nerve fibers will also be affected by the properties of the membrane surface. Thus, it is suggested that the influence of the interfacial region on the of surface-bound molecules should not be disregarded when estimating the proportion of charged and uncharged forms of local anesthetics interacting with axonal membranes. 相似文献
50.
Calli derived from leaves and radicles of B. ternifolia were grown on Murashige and Skoog (MS) basal medium, and the effects of different nitrogen sources on the rate of callus growth and on the enzymes related to nitrogen assimilation were studied. Ammonium alone did not support callus growth unless a Krebs-cycle intermediate was added to the medium. The activities of glutamine synthetase (EC 6.3.1.2), glutamate synthase (EC 1.4.7.1), and glutamate dehydrogenase (EC 1.4.1.2) were measured in homogenates of callus grown on media supplied with different nitrogen sources. The results indicate that leaf and root calli have similar levels of these enzymes when grown on MS medium (Murashige and Skoog 1962. Physiol. Plant. 15, 473–497). However, when the calli were supplied with glutamine as the sole nitrogen source, the activity of glutamate synthase increased in leaf callus but was almost completely inhibited in root callus. The results indicate that calli originated from different B. ternifolia tissues do not have the same biochemical dedifferentiated state. 相似文献