全文获取类型
收费全文 | 8512篇 |
免费 | 637篇 |
国内免费 | 2篇 |
专业分类
9151篇 |
出版年
2023年 | 46篇 |
2022年 | 101篇 |
2021年 | 186篇 |
2020年 | 106篇 |
2019年 | 156篇 |
2018年 | 169篇 |
2017年 | 163篇 |
2016年 | 272篇 |
2015年 | 405篇 |
2014年 | 453篇 |
2013年 | 565篇 |
2012年 | 662篇 |
2011年 | 633篇 |
2010年 | 444篇 |
2009年 | 343篇 |
2008年 | 498篇 |
2007年 | 487篇 |
2006年 | 501篇 |
2005年 | 427篇 |
2004年 | 421篇 |
2003年 | 400篇 |
2002年 | 356篇 |
2001年 | 107篇 |
2000年 | 82篇 |
1999年 | 91篇 |
1998年 | 80篇 |
1997年 | 88篇 |
1996年 | 64篇 |
1995年 | 42篇 |
1994年 | 52篇 |
1993年 | 49篇 |
1992年 | 53篇 |
1991年 | 46篇 |
1990年 | 39篇 |
1989年 | 37篇 |
1988年 | 39篇 |
1987年 | 39篇 |
1986年 | 37篇 |
1985年 | 46篇 |
1984年 | 38篇 |
1983年 | 29篇 |
1982年 | 39篇 |
1981年 | 33篇 |
1980年 | 27篇 |
1979年 | 25篇 |
1978年 | 15篇 |
1977年 | 16篇 |
1976年 | 14篇 |
1975年 | 14篇 |
1973年 | 18篇 |
排序方式: 共有9151条查询结果,搜索用时 12 毫秒
21.
Mario Prandini Gemma Gherson Alessandro Salvaterra Giulio Benamati Gino Zambanini Silvia Conci 《Aerobiologia》1992,8(1):38-45
Summary A study to evaluate and define the atmospheric pollen concentration in Trentino was carried out through the aerobiologic sampling in three localities chosen according to their different climatic conditions.1375 patients with pollinosis living in Trentino were studied retrospectively over the period ranging from 1986 to 1988 and selected according to the area they came from.Results have proved that the most allergenic pollen types are the following: Poaceae, Urticaceae (Parietaria), Compositae (Artemisia) and the tree pollen of Betulaceae and Corylaceae (Alnus, Betula, Corylus), and that pollinosis caused by such pollen, types has different features and frequencies according to the different localities.As far as symptoms are concerned, our data shows that rhinoconjuntivitis is more frequent in those patients who are allergic toParietaria while asthma results being more frequent in patients who are allergic to tree pollen. 相似文献
22.
A detailed study of the regulation and evolution of the two classes of patatin genes in Solanum tuberosum L. 总被引:4,自引:0,他引:4
Xiang-Yun Liu Mario Rocha-Sosa Sabine Hummel Lothar Willmitzer Wolf B. Frommer 《Plant molecular biology》1991,17(6):1139-1154
The class-specific expression of patatin genes was investigated by analysing four new patatin genes. A class I patatin gene from cv. Berolina as well as a class I and two class II patatin genes from the monohaploid cultivar AM 80/5793 were isolated and partially sequenced. Sequence comparison indicates rearrangements as the major source for the generation of diversity between the different members of the classes. The expression of single genes was studied in potato plants transformed with chimaeric genes where the putative patatin promoters were fused to the GUS reporter gene. A detailed histochemical analysis reveals that both class I genes are expressed as the previously described class I patatin gene B33 from cv. Berolina [1], i.e. in the starch-containing cells of potato tubers and in sucrose-induced leaves. The class II gene pgT12 shows the same pattern as the previously described class II gene pgT2 [2], i.e. expression in root tips and in the vascular tissue of tubers, whereas no activity was detectable for pgT4. Thus the expression pattern of both classes of genes seems to be stable at least within or even between different cultivars. 相似文献
23.
Ivano Bertini Bertini Luchinat Mario Piccioli Margarita Vicens Oliver Maria Silvia Viezzoli 《European biophysics journal : EBJ》1991,20(5):269-279
Human copper-cobalt superoxide dismutase in the reduced form has been investigated through 1H NMR techniques. The aim is to monitor the structural properties of this derivative and to compare them with those of reduced and oxidized native superoxide dismutases. The observed signals of the cobalt ligands have been assigned as well as the signals of the histidines bound to copper(I). The latter signals experience little pseudocontact shifts which allow a rough orientation of the magnetic susceptibility tensor in the molecular frame. The connectivities indicate that, although the histidine bridge is broken in the reduced form, the interproton distances between ligands of both ions are essentially the same.Abbreviations WEFT
water eliminated Fourier transform
- NOE
nuclear Overhauser effect
- NOESY
NOE spectroscopy
- COSY
correlation spectroscopy
- TOCSY
total correlation spectroscopy
- SOD
superoxide dismutase
- E2Co(II)SOD
SOD with empty copper site (E=empty) and with cobalt(II) in the Zinc(II) site
Offprint requests to: I. Bertini 相似文献
24.
25.
Mario Lachapelle Moise Bendayan 《Virchows Archiv. B, Cell pathology including molecular pathology》1991,60(1):105-111
Actin and alpha-actinin immunoreactive sites have been localized at the electron microscope level by the protein A-gold immunocytochemical
technique in podocytes of normal and nephrotic rat renal tissues. In normal renal glomeruli, fibrillar networks located in
the core of foot processes or bundles of micro filaments interconnecting them were found to be labelled for these two cytoskeletal
proteins. On the other hand, in nephrotic renal glomeruli, concomitant with the loss of podocytic foot processes a reorganization
of the podocytic cytoskeleton and a concentration of some of its elements into thick uniform bands was observed. Actin and
alpha-actinin were revealed in these bands. Control experiments confirmed the specificity of the labelling obtained. Our results
suggest that normal podocytes contain an actin-based contractile system that might contribute to the maintenance of the particular
cell shape of these cells and that the rearrangement of the podocytic cyto-skeleton occurring in the nephrotic syndrome might
account for the changes in the foot processes and contribute to the alteration in glomerular function.
This work was supported by grants from the Medical Research Council of Canada 相似文献
26.
H Rivera M Moller L M Baltazar A Escalante-Herrera D Garcia-Cruz 《Annales de génétique》1988,31(4):244-246
A 24-year-old female with a Swyer syndrome phenotype was found to have a 46,X,del (Y) (p11) karyotype. This observation is consistent with the recently confirmed assignment of the testis-determining master gene to the deletion interval 1A of the Y (Page et al., 1987). Otherwise, it illustrates the etiological heterogeneity of the Swyer phenotype and allows to emphasize the de novo origin of XYp-females. 相似文献
27.
Isolation of fecal coliforms from pristine sites in a tropical rain forest. 总被引:6,自引:4,他引:2
下载免费PDF全文
![点击此处可从《Applied microbiology》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Samples collected from water accumulated in leaf axilae of bromeliads (epiphytic flora) in a tropical rain forest were found to harbor fecal coliforms. Random identification of fecal coliform-positive isolates demonstrated the presence of Escherichia coli. This bacterium was also isolated from bromeliad leaf surfaces. These data indicate that E. coli may be part of the phyllosphere microflora and not simply a transient bacterium of this habitat. The isolation of fecal coliforms from these sites was unexpected and raises questions as to the validity of using fecal coliforms as indicators of biological water quality in the tropics. 相似文献
28.
Rogelio O. Arellano Fidel Ramón Amelia Rivera Guido A. Zampighi 《The Journal of membrane biology》1986,94(3):293-299
Summary The effect of pH was tested on the junction between crayfish lateral axons. By means of a glass capillary inserted into one of the axons, one side of the nunction was perfused with solutions of known pH while the junctional resistance,R
j, was monitored. Integrity of the gap junction was checked electron microscopically.R
j remained unchanged when the pH of the perfusate was lowered from 7.1 to 6.0. However, when the pH of the unperfused side of the junction was lowered by substituting acetate for chloride in the external solution,R
j rose, attesting to the integrity of the junction and its capacity to uncouple in the perfused state. We suggest that H+ does not affect the junctional channels directly, but acts through an intermediary which is inactivated or removed by the perfusion. 相似文献
29.
F Rivas D García-Cruz H Rivera M L Plascencia R M González J M Cantú 《Annales de génétique》1985,28(2):113-115
A 2 4/12-year-old girl whith a de novo 46,XX,-22 + der(22), t(19;22)(q13.2;p11) karyotype is described. From this and other eight similar cases previously published, a typical phenotype in distal 19q trisomy is concluded. 相似文献
30.
Domenico Osella Silvio Aime Danilo Boccardo Mario Castiglioni Luciano Milone 《Inorganica chimica acta》1985,100(1):97-105
The [Co2(CO)6(RC2R′)] complexes (R, R′ = H, Me, Et, Prn) react with molecular hydrogen under mild conditions of temperature and pressure, at low but appreciable rates. The effect of the steric hindrance of the substituents and the strength of the metalcarbon bonds are discussed. The kinetic data measured for [Co2(CO)6(HC2H)], suggest that both H2-coordination and CO-dissociation are involved in the rate-determining step of the overall hydrogenation process.The catalytic activity of [Co2(CO)6(HC2H)] in the homogeneous hydrogenation of acetylene is described. At low substrate/catalyst ratio the initial hydrogenation rate is equal, within experimental error, to that found for the stoichiometric reaction; on increasing the acetylene concentration, cyclotrimerization to benzene becomes the dominant process. Interestingly C4 hydrocarbons (mainly butadiene and 1-butene) are produced in measurable yield (?8%). The formation of these products is interpreted as the result of the hydrogenation of the elusive [Co2(CO)5(HC2H)2] complex, an unstable intermediate in the cyclotrimerization chain. 相似文献