全文获取类型
收费全文 | 2347篇 |
免费 | 151篇 |
出版年
2023年 | 5篇 |
2022年 | 9篇 |
2021年 | 45篇 |
2020年 | 28篇 |
2019年 | 36篇 |
2018年 | 59篇 |
2017年 | 32篇 |
2016年 | 67篇 |
2015年 | 105篇 |
2014年 | 104篇 |
2013年 | 186篇 |
2012年 | 198篇 |
2011年 | 176篇 |
2010年 | 98篇 |
2009年 | 96篇 |
2008年 | 146篇 |
2007年 | 135篇 |
2006年 | 128篇 |
2005年 | 105篇 |
2004年 | 118篇 |
2003年 | 110篇 |
2002年 | 98篇 |
2001年 | 30篇 |
2000年 | 21篇 |
1999年 | 27篇 |
1998年 | 27篇 |
1997年 | 19篇 |
1996年 | 22篇 |
1995年 | 16篇 |
1994年 | 20篇 |
1993年 | 24篇 |
1992年 | 19篇 |
1991年 | 21篇 |
1990年 | 22篇 |
1989年 | 6篇 |
1988年 | 11篇 |
1987年 | 6篇 |
1986年 | 5篇 |
1985年 | 20篇 |
1984年 | 7篇 |
1983年 | 13篇 |
1982年 | 8篇 |
1981年 | 14篇 |
1980年 | 5篇 |
1979年 | 10篇 |
1978年 | 9篇 |
1974年 | 4篇 |
1971年 | 3篇 |
1970年 | 3篇 |
1968年 | 4篇 |
排序方式: 共有2498条查询结果,搜索用时 31 毫秒
1.
Adriana Calderaro Giovanna Piccolo Chiara Gorrini Sara Montecchini Sabina Rossi Maria Cristina Medici Carlo Chezzi Georges Snounou 《PloS one》2012,7(10)
It has been proposed that ovale malaria in humans is caused by two closely related but distinct species of malaria parasites: P. ovale curtisi and P. ovale wallikeri. We have extended and optimized a Real-time PCR assay targeting the parasite’s small subunit ribosomal RNA (ssrRNA) gene to detect both these species. When the assay was applied to 31 archival blood samples from patients diagnosed with P. ovale, it was found that the infection in 20 was due to P. ovale curtisi and in the remaining 11 to P. ovale wallikeri. Thus, this assay provides a useful tool that can be applied to epidemiological investigations of the two newly recognized distinct P. ovale species, that might reveal if these species also differ in their clinical manifestation, drugs susceptibility and relapse periodicity. The results presented confirm that P. ovale wallikeri is not confined to Southeast Asia, since the majority of the patients analyzed in this study had acquired their P. ovale infection in African countries, mostly situated in West Africa. 相似文献
2.
Twenty-eight strains of pectolytic clostridia were isolated from sugar beet pulp silages. Seventeen non-pigmented strains were presumed to be Clostridium acetobutylicum ; the remaining 11 pigmented strains were similar to Cl. felsineum. The addition of molasses to sugar beet pulps favoured the growth of other bacteria, particularly lactic acid organisms, whereas pectolytic clostridia were only occasionally found. The pectolytic clostridia promoted the structure loss of simulated silages. The use of molasses in sugar beet pulp ensiling was suggested to prevent texture loss of the ensiled mass. 相似文献
3.
4.
5.
Valerio Vidotto Giuseppe Picerno Stefano Caramello Giovanna Paniate 《Mycopathologia》1988,104(3):129-135
The passage between the yeast and mycelial forms of Candida albicans B 311-10 was studied by using the minimal syntehtic medium of Shepherd et al. [19] modified without biotin and with low glucose concentrations. It was observed that biotin, aminoacids and particularly pH are not important factors in the dimorphism of C. albicans. The only factor of notable importance in the passage of yeast form to mycelial form in C. albicans was glucose concentration. 相似文献
6.
Development of tool use in a macaque and a gorilla 总被引:3,自引:0,他引:3
Francesco Natale Patrizia Poti' Giovanna Spinozzi 《Primates; journal of primatology》1988,29(3):413-416
The development of the capacity to use a stick as a tool was tested in a macaque (Macaca fuscata) and a gorilla (Gorilla gorilla gorilla) infants that had previously shown to be able to use strings and supports as dragging tools. Subjects were tested between
15 and 38 months of age. Different levels of competence between the subjects emerged over testing. The macaque developed a
stereotyped strategy to cope with the problem, only getting random successes, whilst the gorilla developed a flexible strategy
and revealed to be able to mentally represent the solution of the problem. In fact, when not successful using the stick, the
gorilla thought out an alternative strategy, choosing and adapting a new object to use it as a tool. 相似文献
7.
Direct observation by X-ray analysis of the tetrahedral "intermediate" of aspartic proteinases. 总被引:1,自引:1,他引:0 下载免费PDF全文
B. Veerapandian J. B. Cooper A. Sali T. L. Blundell R. L. Rosati B. W. Dominy D. B. Damon D. J. Hoover 《Protein science : a publication of the Protein Society》1992,1(3):322-328
We report the X-ray analysis at 2.0 A resolution for crystals of the aspartic proteinase endothiapepsin (EC 3.4.23.6) complexed with a potent difluorostatone-containing tripeptide renin inhibitor (CP-81,282). The scissile bond surrogate, an electrophilic ketone, is hydrated in the complex. The pro-(R) (statine-like) hydroxyl of the tetrahedral carbonyl hydrate is hydrogen-bonded to both active-site aspartates 32 and 215 in the position occupied by a water in the native enzyme. The second hydroxyl oxygen of the hydrate is hydrogen-bonded only to the outer oxygen of Asp 32. These experimental data provide a basis for a model of the tetrahedral intermediate in aspartic proteinase-mediated cleavage of the amide bond. This indicates a mechanism in which Asp 32 is the proton donor and Asp 215 carboxylate polarizes a bound water for nucleophilic attack. The mechanism involves a carboxylate (Asp 32) that is stabilized by extensive hydrogen bonding, rather than an oxyanion derivative of the peptide as in serine proteinase catalysis. 相似文献
8.
9.
Edda De Rossi Giovanna Riccardi Anna Maria Sanangelantoni Orio Ciferri 《FEMS microbiology letters》1985,30(1-2):239-244
Abstract A Spirulina platensis gene library has been constructed using cosmid vector pMMB34. The cosmid bank was controlled for its random gene distribution by colony hybridization. Genes were identified using either homologous or heterologous probes of genes involved in photosynthesis (large and small subunit of d -ribulose 1,5-bisphosphate carboxylase, 32 kDa thylakoid protein, α, β subunits of C-phycocyanin) and protein synthesis (elongation factors EF-Tu, EF-G). 相似文献
10.
We have studied the binding of spermatozoa to the receptor sites on the vitelline coat (VC) of glycerol-treated eggs (ghost eggs) of the Ascidian, Ciona intestinalis (Protochordate). Glycerol treatment cytolyses the egg without affecting the ability of the VC to bind spermatozoa in a species-specific manner; however, in this system binding is not followed by the acrosome reaction. The ghost eggs are metabolically inert. As a base line for our analysis, we have studied the concentration-dependent heat evolved and oxygen consumption of spermatozoa when diluted in sea water. The process has been analyzed on the basis of equations derived by Liquori and Tripiciano to describe cell growth. Upon binding to the ghost eggs, the spermatozoa produce an explosive heat evolution (excess heat) which is not accompanied by oxygen consumption. The excess heat produced plotted against sperm concentration (at constant egg concentrations) gives an asymmetric bell-shaped curve. This is interpreted as being due to the competitive effect of sperm agglutination at a high sperm concentration. It is concluded that only spermatozoa that attach singly (monomeric spermatozoa) to the egg undergo metabolic activation. 相似文献