全文获取类型
收费全文 | 3682篇 |
免费 | 397篇 |
国内免费 | 3篇 |
出版年
2021年 | 36篇 |
2019年 | 30篇 |
2018年 | 22篇 |
2017年 | 43篇 |
2016年 | 48篇 |
2015年 | 84篇 |
2014年 | 85篇 |
2013年 | 163篇 |
2012年 | 161篇 |
2011年 | 164篇 |
2010年 | 129篇 |
2009年 | 94篇 |
2008年 | 130篇 |
2007年 | 156篇 |
2006年 | 117篇 |
2005年 | 132篇 |
2004年 | 178篇 |
2003年 | 143篇 |
2002年 | 176篇 |
2001年 | 116篇 |
2000年 | 143篇 |
1999年 | 95篇 |
1998年 | 59篇 |
1997年 | 50篇 |
1996年 | 50篇 |
1995年 | 52篇 |
1994年 | 43篇 |
1993年 | 44篇 |
1992年 | 58篇 |
1991年 | 58篇 |
1990年 | 42篇 |
1989年 | 53篇 |
1988年 | 49篇 |
1987年 | 39篇 |
1986年 | 43篇 |
1985年 | 34篇 |
1984年 | 53篇 |
1983年 | 41篇 |
1982年 | 53篇 |
1981年 | 47篇 |
1980年 | 49篇 |
1979年 | 33篇 |
1978年 | 51篇 |
1977年 | 33篇 |
1976年 | 47篇 |
1975年 | 41篇 |
1974年 | 41篇 |
1973年 | 34篇 |
1972年 | 24篇 |
1961年 | 21篇 |
排序方式: 共有4082条查询结果,搜索用时 31 毫秒
1.
J R van Der Ploeg R Iwanicka-Nowicka T Bykowski M M Hryniewicz T Leisinger 《The Journal of biological chemistry》1999,274(41):29358-29365
2.
Summary The iliofibularis muscle ofXenopus laevis is reported to contain five types of fibres which have different force—velocity relationships. Ten fibres of each type were selected on the basis of succinate dehydrogenase activity, cross-sectional area and location in the muscle, in order to assess the validity of the fibre type classification.Maximum calcium-stimulated myofibrillar ATPase activity (V
max) and apparent Michaelis constant (K
m) for ATP were determined for these 50 fibres from serial sections. The values obtained varied according to the type of fibre. Type 1 had the highest and type 5 the lowest values forK
m andV
max.In a separate experiment, single freeze-dried fibres were used to determine the relationship between their ATP content and apparentK
m for ATP. There was a tendency for high ATP concentrations in fibres with highK
m values.When myofibrillar ATPase activity was related to the maximum velocity of shortening of the five fibre types, a significant correlation was found. It is concluded that calcium-stimulated myofibrillar ATPase histochemistry allows an estimate of the maximum shortening velocity of muscle fibres fromXenopus laevis. 相似文献
3.
Maurice Campbell 《BMJ (Clinical research ed.)》1948,2(4579):669-671
4.
L Chaerle W Van Caeneghem E Messens H Lambers M Van Montagu D Van Der Straeten 《Nature biotechnology》1999,17(8):813-816
Salicylic acid (SA), produced by plants as a signal in defense against pathogens, induces metabolic heating mediated by alternative respiration in flowers of thermogenic plants, and, when exogenously applied, increases leaf temperature in nonthermogenic plants. We have postulated that the latter phenomenon would be detectable when SA is synthesized locally in plant leaves. Here, resistance to tobacco mosaic virus (TMV) was monitored thermographically before any disease symptoms became visible on tobacco leaves. Spots of elevated temperature that were confined to the place of infection increased in intensity from 8 h before the onset of visible cell death, and remained detectable as a halo around the ongoing necrosis. Salicylic acid accumulates during the prenecrotic phase in TMV-infected tobacco and is known to induce stomatal closure in certain species. We show that the time course of SA accumulation correlates with the evolution of both localized thermal effect and stomatal closure. Since the contribution of leaf respiration is marginal, we concluded that the thermal effect results predominantly from localized, SA-induced stomatal closure. The presymptomatic temperature increase could be of general significance in incompatible plant-pathogen interactions. 相似文献
5.
Alain Dejean Arthur Compin Jacques H. C. Delabie Frdric Azmar Bruno Corbara Maurice Leponce 《Ecological Entomology》2019,44(4):560-570
1. Ants are widespread in tropical rainforests, including in the canopy where territorially dominant arboreal species represent the main part of the arthropod biomass. 2. By mapping the territories of dominant arboreal ant species and using a null model analysis and a pairwise approach this study was able to show the presence of an ant mosaic on the upper canopy of a primary Neotropical rainforest (c. 1 ha sampled; 157 tall trees from 28 families). Although Neotropical rainforest canopies are frequently irregular, with tree crowns at different heights breaking the continuity of the territories of dominant ants, the latter are preserved via underground galleries or trails laid on the ground. 3. The distribution of the trees influences the structure of the ant mosaic, something related to the attractiveness of tree taxa for certain arboreal ant species rather than others. 4. Small‐scale natural disturbances, most likely strong winds in the area studied (presence of canopy gaps), play a role by favouring the presence of two ant species typical of secondary formations: Camponotus femoratus and Crematogaster levior, which live in parabiosis (i.e. share territories and nests but lodge in different cavities) and build conspicuous ant gardens. In addition, pioneer Cecropia myrmecophytic trees were recorded. 相似文献
6.
G. Van Der Velde L. A. Van Der Heijden P. A. J. Van Grunsven P. M. M. Bexkens 《Aquatic Ecology》1982,16(1):51-60
Summary In this paper the leaf-marking method as used for the study of the development and initial decomposition of floating leaves is described and the reliability of the various measurements is tested and/or discussed. Some general results obtained withNymphoides peltata (Gmel.) O. Kuntze in tanks and in the field are presented and crltically discussed. Autolysis followed by microbial decay was in all cases the most important factor by which leaves disintegrated. In the field plots animals were responsible for the disappearance of 22% of the total leaf area produced during a growth season. This is, however, the combined effect of consumption and damage succeeded by microbial decay. Real grazing can be estimated to be no more than 10% of the production of floating leaves. Fungi can have an important role in initial decomposition, especially after the flowering period, as is demonstrated forSeptoria villarsiae Desm. All damage types show temporal and, in the case of animals, also spatial distribution patterns. 相似文献
7.
M A Danilovski? A V Tokarev B I Klement'ev G A Vartanian 《Biulleten' eksperimental'no? biologii i meditsiny》1985,100(8):132-135
The peptide nature of the posture asymmetry factor (PAF) produced in the brain after unilateral removal of the motor region of the neocortex was established. The inactivation of PAF activity in the brain toward the end of the third week after the removal is due to PAF inactivation by the endogenous factor absent from the intact brain. The molecular weight of the inactivation factor exceeds 5.0 kD that makes it possible to separate it from the PAF by gel filtration on Sephadex G-25. The correlation was marked between the increasing activity of the PAF inactivation factor and the recovery of the initial symmetric functioning of the spinal centers during three weeks after unilateral damage to the CNS. 相似文献
8.
Dealing with patients'' sex-related complaints is uncomfortable for many physicians. It can become more comfortable if the physician learns to apply his or her clinical knowledge of sexuality in combination with specific interpersonal interviewing skills. The level of comfort can be increased if the physician accepts his or her professional limitations in providing therapy and knows what other sources of care are available. 相似文献
9.
A R Martikian G S Vartanian K G Karagezian 《Biulleten' eksperimental'no? biologii i meditsiny》1984,98(7):33-35
A study was made of the fatty acid composition and the content of triglycerides, phospholipids and nonesterified fatty acids (NFA) in adipose and muscle tissues of rats with alloxan diabetes. The concentration of NFA in alloxan diabetes was found to be considerably reduced in both adipose and muscle tissues. Meanwhile the content of NFA and phospholipids did not experience any substantial changes. The fatty acid composition of triglycerides of the tissues under study was characterized by considerable alterations under diabetes. 相似文献
10.