全文获取类型
收费全文 | 1305篇 |
免费 | 163篇 |
国内免费 | 3篇 |
出版年
2021年 | 23篇 |
2019年 | 11篇 |
2018年 | 21篇 |
2017年 | 23篇 |
2016年 | 23篇 |
2015年 | 40篇 |
2014年 | 41篇 |
2013年 | 70篇 |
2012年 | 70篇 |
2011年 | 57篇 |
2010年 | 40篇 |
2009年 | 41篇 |
2008年 | 63篇 |
2007年 | 51篇 |
2006年 | 37篇 |
2005年 | 48篇 |
2004年 | 33篇 |
2003年 | 36篇 |
2002年 | 34篇 |
2001年 | 37篇 |
2000年 | 25篇 |
1999年 | 27篇 |
1998年 | 16篇 |
1997年 | 30篇 |
1996年 | 16篇 |
1995年 | 12篇 |
1994年 | 12篇 |
1993年 | 13篇 |
1992年 | 21篇 |
1991年 | 32篇 |
1990年 | 12篇 |
1989年 | 27篇 |
1988年 | 21篇 |
1987年 | 24篇 |
1986年 | 27篇 |
1985年 | 25篇 |
1984年 | 20篇 |
1982年 | 16篇 |
1981年 | 13篇 |
1979年 | 10篇 |
1978年 | 15篇 |
1977年 | 21篇 |
1975年 | 11篇 |
1974年 | 14篇 |
1972年 | 15篇 |
1971年 | 12篇 |
1969年 | 14篇 |
1968年 | 11篇 |
1967年 | 10篇 |
1965年 | 10篇 |
排序方式: 共有1471条查询结果,搜索用时 15 毫秒
1.
Levels of 7.8, 18.5 and 26 mole % deuterium oxide were administered sequentially to (Japanese quail) via the drinking water. The primary effect observed was on egg frequency, which decreased from a normal level of 0.89 for 7.8 mole % D2O to a low of 0.38 during the administration of 26 mole % D2O. Adverse symptoms, such as hyperexcitability, convulsions, skin ulcerations, comatosity, weight loss, or death, which have been associated with deuterium toxicity in other animals, were not observed in these experiments. The amount of deuterium deposited in the water of the egg was 6.9, 13.98, and 19.83 mole % when 7.8, 18.5 and 26 mole % deuterium respectively was administered. For each period, the deuterium content of egg water rapidly reached a maximum concentration after which the concentration decreased slightly. This dilution effect has not been noted previously in body fluids from other animals. 相似文献
2.
Procedure and Analysis of a Useful Method in Determining Mycelial Dry Weights from Agar Plates 下载免费PDF全文
The evaluation of growth by dry weight determination of fungus mycelium for agar plates was examined. The data obtained were statistically analyzed. This method was shown to be sufficiently accurate to be used as an investigative tool. 相似文献
3.
4.
Summary The effects were studied of hydrogen-ion concentration, calcium and manganese supply on the yield of lucerne in both agar and water culture. One agar experiment allowed the effects of two light intensities and two temperatures, on these factors, to be investigated.The toxicity of pH 4 was found to vary, and calcium and nitrogen levels, culture method and climatic conditions were considered contributory factors. The high manganese supply was also found to vary in its toxicity, the most adverse effects being at pH 6, a low calcium supply and a high light intensity. Where the toxicity was most severe the usual orange-brown spotting symptoms were replaced by a chlorosis. Some chemical analyses of the manganese contents of the plants grown under these conditions are reported.The data given here are taken from the thesis submitted by C. D. Sutton for the degree of Ph. D. of the University of Nottingham. 相似文献
5.
Studies of the Growth in Culture of Excised Wheat Roots 总被引:1,自引:0,他引:1
6.
W E Collins J C Skinner M Pappaioanou N S Ma J R Broderson B B Sutton P S Stanfill 《The Journal of parasitology》1987,73(3):536-540
Twenty splenectomized Aotus vociferans (karyotype V) monkeys were infected with strains of Plasmodium vivax from New Guinea, North Korea, Indonesia, El Salvador, and Honduras. Peak parasite densities ranged from 4,840 to 75,500 per mm3. Gametocytes infective to different species of mosquitoes were produced with all strains of P. vivax studied. Two transmissions of the Chesson strain of P. vivax were made by the intravenous inoculation of dissected sporozoites from An. dirus mosquitoes. Prepatent periods were 16 days. 相似文献
7.
An X-ray-crystallographic study of beta-lactamase II from Bacillus cereus at 0.35 nm resolution. 总被引:11,自引:2,他引:9 下载免费PDF全文
B J Sutton P J Artymiuk A E Cordero-Borboa C Little D C Phillips S G Waley 《The Biochemical journal》1987,248(1):181-188
Crystals of beta-lactamase II (EC 3.5.2.6., 'penicillinase') from Bacillus cereus were grown with Cd(II) in place of the natural Zn(II) cofactor and stabilized by cross-linking with glutaraldehyde. Their space group is C2, the cell dimensions are a = 5.44 nm, b = 6.38 nm, c = 7.09 nm and beta = 93.6 degrees, and there is one molecule in the asymmetric unit. Diffraction data were collected from cross-linked crystals of the Cd(II)-enzyme, the apoenzyme and six heavy-atom derivatives. The electron-density map calculated at 0.35 nm resolution reveals the essential Cd(II) ion surrounded by three histidine residues and one cysteine residue. The position of a glutamic acid residue, modification of which destroys activity [Little, Emanuel, Gagnon & Waley (1986) Biochem. J. 233, 465-469], suggests the probable location of the active site of the enzyme. Two minor Cd(II) sites not essential for activity were also located. The structure of the apoenzyme at this resolution appears to differ from that of the Cd(II)-enzyme only in the orientation of two of the histidine residues and the cysteine residue that surround the metal ion. 相似文献
8.
Résumé
Heteroxynema (Cavioxyura) viscaciae n. sp., parasite du caecum et du gros intestin d'un rongeur caviomorphe d' Argentine, Lagidium viscacia boxi Thomas, est décrit. Cette nouvelle espèce est très proche de Heteroxynema (Cavioxyura) chiliensis Quentin, 1975, parasite d' Octodon degus (Molina) au Chili, dont elle se distingue essentiellement par ses mensurations et par la disposition de certaines papilles génitales des mâles. L'étude de cette nouvelle espèce montre l'existence: (i) au niveau des structures buccales d'un dimorphisme sexuel d'un type peu fréquent chez les Oxyuroidea; (ii) de quatre paires seulement de papilles génitales mâles voisinant avec des reliefs cuticulaires qui, dans d'autres espèces, ont peut-être été confondus avec des terminaisons nerveuses supplémentaires; (iii) d'un gubernaculum et d'un spicule, organes rarement observés chez les Heteroxynematidae, mais dont la présence dans d'autres espèces du groupe pourrait avoir été ignorée; (iv) au niveau de l'ovéjecteur, d'un sphincter particulièrement différencié et développé.
Heteroxynema (Cavioxyura) viscaciae n. sp., parasitic in the caecum and large intestine of Lagidium viscacia boxi Thomas, is described. The most closely related species is Heteroxynema (Cavioxyura) chiliensis Quentin, 1975, a parasite of Octodon degus (Molina) from Chile, from which the new species differs by its measurements and disposition of the male's genital papillae. Study of this new species shows the existence of: (i) a type of sexual dimorphism infrequent in the Oxyuroidea, at the level of the buccal structures; (ii) only four pairs of male genital papillae adjoining cuticular protuberances which in other species may have been confused with supplementary nerve endings; (iii) a gubernaculum and a spicule, structures infrequently observed in the Heteroxynematidae, and possibly overlooked or ignored in other species; (iv) a sphincter which is strongly differentiated and developed.
Resumen Se describe a Heteroxynema (Cavioxyura) viscaciae n. sp. paràsito del ciego intestino grueso del rodeor Lagidium viscacia boxi Thomas. Esta nueva especie se asemeja a Heteroxynema (Cavioxyura) chiliensis Quentin, 1975, paràsito de Octodon degus (Molina) de Chile de la cual se diferencie esencialmente por sus medidas y por la disposicion de las papilas genitales del macho. El estudio de esta nueva especie muestra la existencia de: (i) un tipo poco frecuente en los Oxyuroidea de dimorfismo sexual a nivel de las estructuras bucales; (ii) cuatro pares de papilas genitales en el macho ubicadas proximas a relieves cuticulares que en otras especies pueden haber sido confundidos con terminaciones nerviosas suplementarias; (iii) de un gubernàculo y una espicula, organos raramente observables en los Heteroxynematidae, pero cuya presencia en otras especies del grupo pudo haber sido ignorada; (iv) de un sphincter particularmente diferenciado y desarollado.相似文献
9.
We report the first study of the effect of NaCl on the double-bond isomeric composition of fatty acids and theirsn-1/sn-2 positional distribution in the membrane phospholipids of a moderately halophilic eubacterium. The major phospholipids, phosphatidylethanolamine and phosphatidylglycerol, ofVibrio costicola grown in 1M or 3M NaCl both have ansn-1 saturated,sn-2 unsaturated distribution of fatty acids. There is a greater effect of salinity on the fatty acid composition of phosphatidylglycerol compared with phosphatidylethanolamine. The fatty acids in phosphatidylethanolamine of cultures grown in 1M compared with 3M NaCl have the same unsaturation index and average chain length, but different double-bond isomeric compositions. In comparison, the fatty acid composition of phosphatidylglycerol is more unsaturated, with a different double-bond isomeric distribution, and has a shorter average chain length in cultures grown in 3M compared with 1M NaCl. The pattern of fatty acid isomers of 16:1 and 18:1 shows thatV. costicola uses the anaerobic pathway of fatty acid biosynthesis. The presence of the isomers 16:1c11 and 18:1c13 in the phospholipids of cultures grown in 3M but not in 1M NaCl indicates that external salinity affects the specificity of fatty acid synthetase in this moderately halophilic bacterium. 相似文献
10.