全文获取类型
收费全文 | 7509篇 |
免费 | 496篇 |
国内免费 | 1篇 |
出版年
2023年 | 28篇 |
2022年 | 72篇 |
2021年 | 151篇 |
2020年 | 95篇 |
2019年 | 126篇 |
2018年 | 193篇 |
2017年 | 164篇 |
2016年 | 234篇 |
2015年 | 378篇 |
2014年 | 443篇 |
2013年 | 569篇 |
2012年 | 655篇 |
2011年 | 650篇 |
2010年 | 376篇 |
2009年 | 401篇 |
2008年 | 497篇 |
2007年 | 453篇 |
2006年 | 467篇 |
2005年 | 367篇 |
2004年 | 398篇 |
2003年 | 329篇 |
2002年 | 331篇 |
2001年 | 65篇 |
2000年 | 52篇 |
1999年 | 51篇 |
1998年 | 60篇 |
1997年 | 46篇 |
1996年 | 42篇 |
1995年 | 34篇 |
1994年 | 23篇 |
1993年 | 25篇 |
1992年 | 29篇 |
1991年 | 23篇 |
1990年 | 27篇 |
1989年 | 19篇 |
1988年 | 21篇 |
1987年 | 9篇 |
1986年 | 13篇 |
1985年 | 19篇 |
1984年 | 15篇 |
1983年 | 7篇 |
1982年 | 12篇 |
1981年 | 8篇 |
1980年 | 2篇 |
1979年 | 5篇 |
1978年 | 2篇 |
1977年 | 4篇 |
1974年 | 4篇 |
1967年 | 2篇 |
1929年 | 1篇 |
排序方式: 共有8006条查询结果,搜索用时 15 毫秒
71.
72.
Silvia M.C. Dias João B. Fernandes José G.S. Maia Otto R. Gottlieb Hugo E. Gottlieb 《Phytochemistry》1982,21(7):1737-1740
The trunk wood of an Amazonian Aniba (Lauraceae) species contains, besides dillapiol and the benzodioxane-type neolignan eusiderin, four bicyclo(3.2.1)octanoid neolignans. These comprise representatives of the canellin-type: the known methoxycanellin-A and the novel compounds characterized as (1R, 3S, 4S, 5S, 6S, 7R)-1-allyl-4-hydroxy-3, 5-dimethoxy-7-methyl-6-(3′-methoxy-4′, 5′-methylenedioxyphenyl)-8-oxo-bicyclo(3.2.1)octane; (1R, 3S, 4S, 5S, 6S, 7R)-1-allyl-4-hydroxy-3, 5-dimethoxy-7-methyl-6-(3′, 4′, 5′-trimethoxyphenyl)-8-oxobicyclo(3.2.1)octane and (1R, 4R, 5R, 6S, 7R, 8S)-1-allyl-4, 8-dihydroxy-5-methoxy-7-methyl-6-(3′-methoxy-4′,5′-methylenedioxyphenyl)-3-oxobicyclo(3.2.1)octane. 相似文献
73.
Among more than 50 isolates ofBacillus thuringiensis Berliner (B.t.) tested, 7 incited 100% mortality when 2nd instar larvae ofSpodoptera littoralis Boisduval were fed on alfalfa leaves dipped in a spore-crystal suspension of 108 colony forming units/ml. Among those isolates,B.t. 24 demonstrated the highest activity. Larvae of instars 1 and 2 were the most susceptible toB.t. Susceptibility decreased with larval development. However, larvae of all instars were killed by isolateB.t. 24. Larvae that survived after feeding withB.t. 24 were retarded and fed less. Their weight relative to the controls was lower as the spore concentration on the leaves on which they fed was higher. Survival of the spores in the field dropped drastically to 2% after 4 days. Insecticidal activity of the sprayed suspension on those leaves, however, remained significant.B.t. 24 was also effective against larvae on cotton plants in the greenhouse and in a preliminary field experiment. Numbers of colony forming units recovered from leaves dipped in suspension of various spore concentrations showed significant correlation with the initial concentrations as did sprayed leaves. However, colony forming units recovered from sprayed leaves were 5–7.5 fold lower than from dipped leaves. Dipped cotton leaves showed 3.1×10?5 ml attached to 1 mm2 leaf surface whereas sprayed ones had 6×10?6 ml. Those data are important for the determination of spore concentrations in suspensions required for spraying. The isolateB.t. 24 was serotyped byH. de Barjac as H-6B. thuringiensis entomocidus. 相似文献
74.
Collagen phenotypes were determined for rabbit articular chondrocytes in cartilage slices and first through fifth monolayer cultures. During the first 24 hr of slice culture, chondrocytes exhibited the following collagen phenotype: 96% type II, 3% X2Y and 1% type III. In primary monolayer culture, no other types of collagen were added to this differentiated chondrocyte phenotype; however, the synthesis per cell of each of the expressed collagens was stimulated. By the fifth day of primary culture, X2Y synthesis increased 10 fold, and by the eighth day, a further 4 fold. In contrast, the synthesis of collagen types II and III showed no change by the fifth day, but increased 7 fold by the eighth day. These results suggest independent regulation of X2Y in this situation. In a separate experiment, first through fifth cultures were studied. The synthesis per cell of type II collagen declined steadily and essentially ceased by the fifth culture, indicating the loss of differentiated function by these chondrocyte progeny. The loss of type II synthesis was not quantitatively replaced by the synthesis of type I trimer and type I collagen which was first detected in the third culture. While these qualitative changes in phenotype occurred, the stimulated rate of type III collagen synthesis did not change and that of X2Y declined only slightly. Thus the termination of type II synthesis did not significantly alter the synthesis of the other collagens produced by differentiated chondrocytes. The final “de-differentiated” phenotype was 41% type I, 25% X2Y, 20% type I trimer, 13% type III and 1% type II. 相似文献
75.
76.
Summary A technique is described for measuring the approximate exchange rates of the more labile amide protons in a protein. The technique relies on a comparison of the intensities in1H–15N correlation spectra recorded with and without presaturation of the water resonance. To distinguish resonance attenuation caused by hydrogen exchange from attenuation caused by cross relation, the experiment is repeated at several different pH values and the difference in attenuation of any particular amide resonance upon presaturation is used for calculating its exchange rate. The technique is demonstrated for calmodulin and for calmodulin complexed with its binding domain of skeletal muscle myosin light chain kinase. Upon complexation, increased amide exchange rates are observed for residues Lys75 through Thr79 located in the central helix of calmodulin, and for the C-terminal residues Ser147 and Lys148. In contrast, a decrease in amide exchange rate is observed at the C-terminal end of the F helix, from residues Thr110 through Glu114.Istituto Guido Donegani, Novara, Italy 相似文献
77.
Mouse Cx50, a functional member of the connexin family of gap junction proteins, is the lens fiber protein MP70. 总被引:15,自引:5,他引:10 下载免费PDF全文
The crystalline lens is an attractive system to study the biology of intercellular communication; however, the identity of the structural components of gap junctions in the lens has been controversial. We have cloned a novel member of the connexin family of gap junction proteins, Cx50, and have shown that it is likely to correspond to the previously described lens fiber protein MP70. The N-terminal amino acid sequence of MP70 closely matches the sequence predicted by the clone. Cx50 mRNA is detected only in the lens, among the 12 organs tested, and this distribution is indistinguishable from that of MP70 protein. A monoclonal antibody directed against MP70 and an anti-Cx50 antibody produced against a synthetic peptide identify the same proteins on western blots and produce identical patterns of immunofluorescence on frozen sections of rodent lens. We also show that expression of Cx50 in paired Xenopus oocytes induces high levels of voltage-dependent conductance. This indicates that Cx50 is a functional member of the connexin family with unique physiological properties. With the cloning of Cx50, all known participants in gap junction formation between various cell types in the lens are available for study and reconstitution in experimental systems. 相似文献
78.
79.
N. D. Bruzzone A. P. Economopoulos Hua-Song Wang 《Entomologia Experimentalis et Applicata》1990,56(1):103-106
The standard finisher larval diet used at Seibersdorf for rearing the Mediterranean fruit fly,Ceratitis capitata (Wiedemann), was reused following autoclave heat-treatment to kill larvae or pupae remaining from its first use. Only when the spent diet was mixed with water (about 40% of final diet, w/w) to reconstitute fresh-diet texture, and combined with fresh starter, a similar, but still inferior in respect to larval duration and pupal recovery and size, to the fresh finisher diet production of flies was achieved. Enrichment of the autoclaved spent finisher with small quantities of nutrients gave inconclusive results. Although spent-diet pupae were significantly smaller than fresh-diet control pupae, their adults survived significantly longer than control adults.
Zur massenaufzucht vonCeratitis capitata: die wiesderverwendung der endkomponente der larvendiät
Zusammenfassung Die in Seibersdorf zur Aufzucht der Mittelmeerfruchtfliege,Ceratitis capitata (Wiedemann) (Diptera: Tephritidae), verwendete Standardendkomponente der Larvendiät konnte nach Abtötung der von der Erstverwendung verbliebenen Larven oder Puppen mittels Autoklavensterilisation wiederverwendet werden. Eine zur frischen Kontrolldiät vergleichbare, jedoch bezüglich der Länge des Larvenstadiums, der Entwicklung der Puppen nach dem Schlüpfen sowie der Größe der Puppen noch immer schlechtere Fliegenproduktion wurde erreicht, wenn die wiederverwendete, autoklavierte Diät mit Wasser (ca. 40% der Enddiät, w/w) zwecks Rekonstitution zur frischen Diättexture gemischt und mit frischem Starter kombiniert wurde. Eine Anreicherung der wiederverwendeten Diätendkomponente mit geringen Mengen von Nährstoffen ergab keine schlüssigen Resultate. Obwohl Puppen der wiederverwendeten Diät signifikant kleiner als Puppen der Frischdiät-Kontrolle waren, überlebten deren Erwachsene signifikant länger als die Erwachsenen der Kontrolle.相似文献
80.