全文获取类型
收费全文 | 10701篇 |
免费 | 1035篇 |
国内免费 | 927篇 |
出版年
2024年 | 30篇 |
2023年 | 217篇 |
2022年 | 278篇 |
2021年 | 322篇 |
2020年 | 328篇 |
2019年 | 493篇 |
2018年 | 468篇 |
2017年 | 325篇 |
2016年 | 403篇 |
2015年 | 434篇 |
2014年 | 668篇 |
2013年 | 783篇 |
2012年 | 523篇 |
2011年 | 648篇 |
2010年 | 575篇 |
2009年 | 668篇 |
2008年 | 618篇 |
2007年 | 605篇 |
2006年 | 469篇 |
2005年 | 468篇 |
2004年 | 358篇 |
2003年 | 293篇 |
2002年 | 293篇 |
2001年 | 242篇 |
2000年 | 208篇 |
1999年 | 213篇 |
1998年 | 197篇 |
1997年 | 171篇 |
1996年 | 163篇 |
1995年 | 141篇 |
1994年 | 131篇 |
1993年 | 131篇 |
1992年 | 109篇 |
1991年 | 74篇 |
1990年 | 84篇 |
1989年 | 68篇 |
1988年 | 63篇 |
1987年 | 52篇 |
1986年 | 39篇 |
1985年 | 47篇 |
1984年 | 46篇 |
1983年 | 39篇 |
1982年 | 27篇 |
1981年 | 31篇 |
1980年 | 24篇 |
1979年 | 23篇 |
1978年 | 11篇 |
1977年 | 11篇 |
1976年 | 17篇 |
1974年 | 14篇 |
排序方式: 共有10000条查询结果,搜索用时 125 毫秒
41.
Hypoxia-induced fibre type transformation in rat hindlimb muscles
Histochemical and electro-mechanical changes 总被引:1,自引:0,他引:1
Histochemical and electro-mechanical changes 总被引:1,自引:0,他引:1
Kazuo Itoh Toshio Moritani Koji Ishida Chiyoko Hirofuji Sadayoshi Taguchi Minoru Itoh 《European journal of applied physiology and occupational physiology》1990,60(5):331-336
Twelve male Sprague-Dawley rats (21 days old) were randomly assigned into two experimental groups: sea level control (CONT) and hypobaric hypoxia (HYPO). The HYPO rats were kept in an hypobaric chamber maintaining a simulated altitude of 4000 m (61.1 kPa). After 10 weeks of treatment, the rat hindlimb muscles [soleus (SOL) and extensor digitorum longus (EDL)] were subjected to histochemical and electro-mechanical analyses. Results indicated that compared to CONT the HYPO SOL muscle had a significantly greater relative distribution of fast-twitch-oxidative-glycolytic (FOG) fibres (28.9% SEM 2.0 vs 18.3% SEM 1.8, P less than 0.01) with a significant decrease in slow twitch oxidative fibre distribution (69.5% SEM 2.4 vs 82.9% SEM 3.1, P less than 0.01). Compared to CONT the HYPO EDL muscle also manifested a significant increase in FOG fibre distribution (51.6% SEM 0.8 vs 46.6% SEM 1.1, P less than 0.01), but this was accompanied by a significant decrease in fast twitch glucolytic fibres (44.3% SEM 0.9 vs 49.2% SEM 1.7, P less than 0.05). These histochemical fibre type transformations accompanied significant and expected changes in the electro-mechanical parameters tested in situ, e.g. maximal twitch force, maximal rate of force development, contraction time, half relaxation time, force: frequency curve, and fatigability. It was concluded that chronic hypobaric hypoxia could have a potent influence upon the phenotype expression of muscle fibres. 相似文献
42.
Muscle hypertrophy and fast fiber type conversions in heavy resistance-trained women 总被引:1,自引:0,他引:1
R. S. Staron E. S. Malicky M. J. Leonardi J. E. Falkel F. C. Hagerman G. A. Dudley 《European journal of applied physiology and occupational physiology》1990,60(1):71-79
Twenty-four women completed a 20-week heavy-resistance weight training program for the lower extremity. Workouts were twice a week and consisted of warm-up exercises followed by three sets each of full squats, vertical leg presses, leg extensions, and leg curls. All exercises were performed to failure using 6-8 RM (repetition maximum). Weight training caused a significant increase in maximal isotonic strength (1 RM) for each exercise. After training, there was a decrease in body fat percentage (p less than 0.05), and an increase in lean body mass (p less than 0.05) with no overall change in thigh girth. Biopsies were obtained before and after training from the superficial portion of the vastus lateralis muscle. Sections were prepared for histological and histochemical examination. Six fiber types (I, IC, IIC, IIA, IIAB, and IIB) were distinguished following routine myofibrillar adenosine triphosphatase histochemistry. Areas were determined for fiber types I, IIA, and IIAB + IIB. The heavy-resistance training resulted in significant hypertrophy of all three groups: I (15%), IIA (45%), and IIAB + IIB (57%). These data are similar to those in men and suggest considerable hypertrophy of all major fiber types is also possible in women if exercise intensity and duration are sufficient. In addition, the training resulted in a significant decrease in the percentage of IIB with a concomitant increase in IIA fibers, suggesting that strength training may lead to fiber conversions. 相似文献
43.
Production of novel pullulanases at high concentrations by two newly isolated thermophilic clostridia 总被引:1,自引:0,他引:1
Two thermophilic bacteria, which are capable of growing on starch at 60-70 degrees C under anaerobic conditions, were isolated from a sugar refinery in Uelzen and from Solar lake in Israel. On the basis of their physiological characteristics they were identified as Clostridium thermohydrosulfuricum Uel 1 and C. thermohydrosulfuricum Sol 1, respectively. The product pattern of glucose polymer hydrolysis showed that both strains secreted enzymes that possess amylolytic and pullulytic activities. The major product formed was maltose. In addition, alpha-glucosidase activity could be detected in the supernatants of Uel 1 strain. Compared to most anaerobes investigated these isolates secreted extremely high concentrations of pullulanases in batch culture. Up to 85% of the total enzyme synthesized was detected in the culture fluid. Unlike the pullulanases of type I, which can only attack the alpha-1,6-glycosidic linkages, the pullulanases of both clostridial strains were also capable of hydrolyzing alpha-1,4-linkages. The enzyme system of both bacteria was found to be highly thermoactive; optimal activity was detected at pH 5.0 and 85 degrees C. Even at 95 degrees C and without the addition of metal ions still 15% to 25% of enzymatic activity was detectable. 相似文献
44.
In the Pedregal de San Angel reserve, in Mexico City, males of the butterfly Xamia xamiperch in and defend areas with well-defined topographic limits. These areas lack concentrations of receptive females and of larvae and adult resources. One individual defends the same territory an average of 5 h/day, up to a maximum of 23 days. The same areas are used as territories by different males during the year. These areas share some characteristic features which are described. Evidence is presented in support of the hypothesis that the territories function as mating stations. A possible scenario for the evolution of this territorial mating system is advanced. 相似文献
45.
46.
Mating behavior in seaweed flies (Coelopa frigida) 总被引:1,自引:0,他引:1
47.
Dichogamy and sex allocation in several populations of Campanula microdonta and C. punctata were investigated with regard to their mating systems. Duration of the staminate phase differed among the populations: staminate phase was longer in self-compatible (SC) and largely outcrossing populations than in self-incompatible (SI) and outcrossing populations or in SC and largely inbreeding populations. Duration of the pistillate phase among the populations was less variable than duration of the staminate phase. Male reproductive effort decreased with increase of the estimated selfing rates. Male allocation (weight ratio of androecium to gynoecium or to total flower) may be used as an indicator of the breeding system. Within each population, small flowers allocate proportionately more resources to the androecium than to the gynoecium. Among populations, SC outcrossing populations tend to produce large ovaries, and SC inbreeding populations tend to produce small ovaries. 相似文献
48.
A. M. Tomson R. Demets W. L. Homan D. Stegwee H. van den Ende 《Sexual plant reproduction》1988,1(1):46-50
Summary We describe a circadian rhythm in the surface density of receptors that play a dominant role in the mating process of the unicellular green alga Chlamydomonas eugametos.These receptors — called agglutinins — are large glycoproteins extrinsically bound to the membrane of gamete flagella. We found circadian fluctuations in their density. Since inhibition of protein synthesis affected the agglutinin density without a lag period at any time,we conclude that the density was dependent on de novo synthesis and that the fluctuations in density are caused by circadian oscillations in the rate of agglutinin synthesis. This phenomenon evidently underlies the pronounced endogenous rhythm in mating competence that we described previously (Demets et al. 1987). Finally, we speculate on the nature of the time keeping mechanism that is generating these rhythmic events. 相似文献
49.
The leaf ultrastructure of NADP-malic enzyme type C4 species possessing different anatomical features in the Cyperaceae was examined: types were the Rhynchosporoid type, a normal
Kranz type in which mesophyll cells are adjacent to Kranz cells, and Fimbristyloid and Chlorocyperoid types, unusual Kranz
types in which nonchlorophyllous mestome sheath intervenes between the two types of green cells. They show structural characteristics
basically similar to the NADP-malic enzyme group of C4 grasses, that is, centrifugally located chloroplasts with reduced grana and no increase of mitochondrial frequency in the
Kranz cells. However, the Kranz cell chloroplasts of the Fimbristyloid and Chlorocyperoid types exhibit convoluted thylakoid
systems and a trend of extensive development of peripheral reticulum, although those of the Rhynchosporoid type do not possess
such particular membrane systems. The suberized lamella, probably a barrier for CO2 diffusion, is present in the Kranz cell walls of the Rhynchosporoid type and in the mestome sheath cell walls of the other
two types, and tightly surrounds the Kranz cells (sheaths) that are the sites of the decarboxylation of C4 acids. These ultrastructural features are discussed in relation to C4 photosynthetic function. 相似文献
50.
Detailed examination of a sample plot covered by the Lindero membranaceae-Fagetum crenatae association on Mt. Sanpoiwadake,
Hakusan National Park, revealed a number of correlations between the distribution of subassociations and environmental factors.
The subassociations on the south-facing slopes receive deep snow cover in winter with rapid melting in the spring. They occur
on porous, freely draining soils, typical of the general range of brown forest soils. Conversely, on the north-eastern slopes
there are widespread late-snow patches which delay leaf development and expansion and which provide an abundant water supply
well into early summer. Under these conditions, bleached soil horizons have developed with iron pan formation, resulting in
poor soil drainage, strongly correlated with quite different plant communities. 相似文献