全文获取类型
收费全文 | 3243篇 |
免费 | 234篇 |
出版年
2023年 | 29篇 |
2021年 | 51篇 |
2020年 | 38篇 |
2019年 | 33篇 |
2018年 | 94篇 |
2017年 | 85篇 |
2016年 | 150篇 |
2015年 | 122篇 |
2014年 | 145篇 |
2013年 | 260篇 |
2012年 | 123篇 |
2011年 | 110篇 |
2010年 | 125篇 |
2009年 | 109篇 |
2008年 | 116篇 |
2007年 | 68篇 |
2006年 | 113篇 |
2005年 | 84篇 |
2004年 | 75篇 |
2003年 | 83篇 |
2002年 | 74篇 |
2001年 | 60篇 |
2000年 | 56篇 |
1999年 | 57篇 |
1998年 | 65篇 |
1997年 | 39篇 |
1996年 | 50篇 |
1995年 | 47篇 |
1994年 | 49篇 |
1993年 | 55篇 |
1992年 | 33篇 |
1991年 | 33篇 |
1989年 | 26篇 |
1988年 | 32篇 |
1987年 | 24篇 |
1985年 | 29篇 |
1984年 | 24篇 |
1981年 | 30篇 |
1980年 | 36篇 |
1978年 | 28篇 |
1975年 | 25篇 |
1974年 | 37篇 |
1973年 | 28篇 |
1972年 | 25篇 |
1971年 | 26篇 |
1969年 | 27篇 |
1966年 | 27篇 |
1963年 | 24篇 |
1962年 | 27篇 |
1960年 | 24篇 |
排序方式: 共有3477条查询结果,搜索用时 15 毫秒
11.
12.
Twelve metronidazole-resistant and twelve metronidazole-susceptible strains ofTrichomonas vaginalis were tested for the presence of dsRNA. Three resistant and five susceptible strains were found to contain dsRNA which indicated
that metronidazole resistance does not correlate with the absence of dsRNA. Electron microscopy showed the homogenates of
all dsRNA -positive strains to contain virus-like particles 32 –38 nm in diameter, while no such particles were found in the
dsRNA-negative strains. A mutual relationship between the dsRNA and virus-like particles seems to exist.
After this paper had been accepted for publication the occurrence of virus-like particles in dsRNA-positive trichomonads was
reported by others (Wang A.L., Wang C.C.: The double stranded RNA inTrichomonas vaginalis may originate from virus-like particles.Proc. Nat. Acad. Sci. USA
83, 7956–7961, 1986). 相似文献
13.
Tibor Hortobagyi Frank I. Katch Peter F. LaChance 《European journal of applied physiology and occupational physiology》1989,58(7):749-755
Two studies were conducted in 83 college men to determine the degree of generality of individual differences in upper body muscular strength assessed by different testing modes. In study 1 (N = 43), correlations were computed between four measures of upper body strength using the bench press movement, maximal isokinetic (0.09 rad.s-1), maximal fast (0.126 m.s-1) and slow (0.037 m.s-1) hydraulic, and one repetition maximum (1-RM) free weight bench press (BP). Compared to free weight BP, maximal strength during isokinetic and slow hydraulic BP was approximately 29% and approximately 8% larger, and fast hydraulic BP strength was approximately 63% lower (p less than 0.05). Simple linear regression of isokinetic BP on 1-RM BP yielded r = 0.79, error of prediction (SE) = 12%, and generality = 81%. The corresponding averaged values for the regression of slow and fast hydraulic BP on free weight 1-RM BP were r = 0.77, SE = 13.5%, and generality = 84%. In Study 2 (N = 40), testing included maximal isokinetic concentric and eccentric arm flexion and extension at 0.524, 1.570, and 2.094 rad.s-1. The ratio of concentric to eccentric torque at the 3 speeds averaged 0.68 (flexion) and 0.70 (extension), and eccentric torques were 32% and 30% greater than concentric torques (p less than 0.05). The linear regression between concentric vs. eccentric flexion and extension torques at the three velocities yielded an average r = 0.80, SE = 13.7%, and generality = 73%.(ABSTRACT TRUNCATED AT 250 WORDS) 相似文献
14.
High-performance liquid chromatography was used to estimate 3-ketolactose and 3-ketosucrose in cultures of agrobacteria. The
activities of enzymes that convert the disaccharide substrate were evaluated during batch cultivation ofAgrobacterium tumefaciens on sucrose, maltose, and lactose. The highest activity of glucoside 3-dehydrogenase and a slight activity of disaccharide-hydrolyzing
enzymes were found in cells grown on lactose. Nongrowing cells converted lactose to 3-ketolactose faster than immobilized
cells did. Immobilization of cells into polysaccharide gels did not stabilize the activity of glucoside 3-dehydrogenase. Glutaraldehyde
cross-linking of the cell content led to an inactivation of the respiratory chain but Fe3+ could be used as an electron acceptor. Cells treated with glutaraldehyde converted lactose faster than nongrowing ones but
the activity of glucoside 3-dehydrogenase was not stable. 相似文献
15.
Ivo Šafařík 《Journal of industrial microbiology & biotechnology》1988,3(4):259-261
Summary A new insoluble chromogenic substrate for the determination of proteolytic activity was developed. This substrate was prepared by incorporating black drawing ink into casein and heating this complex at 200°C for 4 h. It is especially suitable for determining the activity of alkaline bacterial proteinases. 相似文献
16.
Gerd Wallukat Gyorgy Nemecz Tibor Farkas Hartmut Kuehn Albert Wollenberger 《Molecular and cellular biochemistry》1991,102(1):35-47
Incubation of rocker-cultured neonatal rat heart cells with 3 mM L(+)-lactate led to a sharp increase in the sensitivity of cardiomyocytes to the beta-adrenergic agonist isoprenaline, as measured by their chronotropic response. This effect was accompanied by a reduction in the arachidonic acid content of the total phospholipids. The phospholipase A2-activator melittin as well as free arachidonic acid induced this supersensitivity to the same degree. On the other hand, the L(+)-lactate-evoked supersensitivity could be blocked by the phospholipase A2 inhibitors mepacrine and n-bromophenacyl-bromide, suggesting an involvement of phospholipase A2 in the process of beta-adrenergic sensitization. The sensitizing action of arachidonic acid was blocked by the lipoxygenase inhibitors esculetin and nordihydroguaiaretic acid, but not by the cyclooxygenase inhibitor indomethacin. Supersensitivity was likewise evoked by 15-S-hydroxyeicosatetraenoic acid (15-S-HETE), but not by 5-S-HPETE or 5-S-HETE. These findings suggest that the phospholipase A2-15-lipoxygenase pathway plays a role in the induction of beta-adrenergic supersensitivity in the cultured cardiomyocytes and point to a new physiological role of the lipoxygenase product 15-S-HETE.Abbreviations NDGA
nordihydroguaiaretic acid
- HETE
hydroeicosatetraenoic acid
- HPETE
hydroperoxyeicosatetraenoic acid 相似文献
17.
J. Koníček M. Koníčková-Radochová G. Y. Daraselia M. Šlosárek 《Folia microbiologica》1988,33(1):71-79
It is generally assumed that genetic research of mycobacteria is delayed as compared with other, more commonly used, bacterial models, particularly in the field of genetic transfers. In the field of mutagenesis the problems have been studied to such an extent that replication maps of the chromosome of M. phlei and M. tuberculosis H37 Rv have already been constructed and a new model of the cell cycle of bacteria exhibiting a slow growth rate has been worked out. When the problems of mycobacterial genetics are looked upon in the light of gene manipulations it may be concluded that mycobacteria belong to a few models whose genes are used for cloning and that problems of practical significance will be studied by means of the most modern approaches. 相似文献
18.
Single and repeated intravenous administration of cyclophosphamide significantly decreased the candidacidal activity of rabbit peritoneal macrophages. Using higher doses of the drug, a more pronounced decrease, persisting up to 10 d, was observed. The phagocytic index has not changed significantly 10 d after cyclophosphamide injection as compared with controls. No changes in the phagocytic activity were recorded. The decreased candidacidal activity may be one of the causes of serious microbial infections in cyclophosphamide-treated patients. 相似文献
19.
Daughter cells of the chlorococcal algaScenedesmus quadricauda incubated under photosynthesizing conditions in a nitrogen-free medium did not make any progress in the cell cycle. Photosynthetic
starch formation continued for a period corresponding to a half of the cell cycle and then levelled off. Protein synthesis
was very slow and it did not surpass double the initial amount. RNA content decayed from the start of treatment and approached
about 2 pg/cell.
When a synchronous population was deprived of nitrogen or of light in the middle of the cell cycle RNA synthesis stopped immediately
or very soon afterwards and, in spite ofabundant intracellular nitrogen reserves, RNA content slowly declined. This degradation
was much extensive in nitrogen starved cells where, eventually, the RNA content attained about half the starting value. In
both experimental variants, DNA replications started at the same time as in control culture, but the final amount of DNA attained
only half the control value. Protein synthesis stopped immediately in the dark. In the nitrogen-starved cells, it continued
for several hours and protein content increased about 70 % of the amount present at the start of starvation. The number of
daughter cells formed was proportional to the final protein content in the nitrogen-and light-deprived cells (corresponding
division numbers were 6 and 4, respectively). Upon refeeding of daughter cells formed under nitrogen starvation, RNA synthesis
started immediately, while protein synthesis displayed a lag of about 5 h. DNA replications were triggered at the time when
the ratio of RNA to DNA content attained the same value as in the control culture. 相似文献
20.