全文获取类型
收费全文 | 50875篇 |
免费 | 3688篇 |
国内免费 | 25篇 |
专业分类
54588篇 |
出版年
2023年 | 185篇 |
2022年 | 585篇 |
2021年 | 946篇 |
2020年 | 594篇 |
2019年 | 722篇 |
2018年 | 1088篇 |
2017年 | 968篇 |
2016年 | 1585篇 |
2015年 | 2456篇 |
2014年 | 2840篇 |
2013年 | 3182篇 |
2012年 | 4197篇 |
2011年 | 3955篇 |
2010年 | 2529篇 |
2009年 | 2315篇 |
2008年 | 3185篇 |
2007年 | 3080篇 |
2006年 | 2692篇 |
2005年 | 2499篇 |
2004年 | 2324篇 |
2003年 | 1999篇 |
2002年 | 1738篇 |
2001年 | 1383篇 |
2000年 | 1324篇 |
1999年 | 1070篇 |
1998年 | 427篇 |
1997年 | 378篇 |
1996年 | 283篇 |
1995年 | 248篇 |
1994年 | 243篇 |
1993年 | 204篇 |
1992年 | 405篇 |
1991年 | 353篇 |
1990年 | 320篇 |
1989年 | 277篇 |
1988年 | 206篇 |
1987年 | 203篇 |
1986年 | 164篇 |
1985年 | 144篇 |
1984年 | 109篇 |
1983年 | 105篇 |
1982年 | 85篇 |
1981年 | 69篇 |
1980年 | 72篇 |
1979年 | 91篇 |
1978年 | 73篇 |
1977年 | 59篇 |
1976年 | 63篇 |
1974年 | 78篇 |
1973年 | 62篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
131.
132.
Christophe Tournamille Caroline Le Van Kim Pierre Gane Jean-Pierre Cartron Yves Colin 《Human genetics》1995,95(4):407-410
Spondyloepiphyseal dysplasia tarda (SEDL) is an X-linked recessive disorder characterized in affected males by short stature resulting from a growth defect of the vertebral bodies. We have extended our earlier studies by analyzing 15 families with newly identified microsatellite DNA markers; analysis of recombination events with these markers indicates that the gene responsible for SEDL is located in Xp22 between DXS 16 and DXS 987 on an interval spanning approximately 2 Mb. 相似文献
133.
The focus of this paper is the study of stability and point-to-point movement of a one-link arm. The sagittal arm has two
musculotendon actuators, two neural oscillators that generate burst signals as motoneuron inputs, and spindles and Golgi tendon
organs for extrinsic reflex feedbacks. It is shown that coactivation leads to intrinsic position and velocity feedback, and
that the tendons introduce intrinsic force and rate of force feedback. In addition, the integrating effects of the tendons
are studied when the actuator is constructed from a large number of identical fibers that are excited by alpha signals whose
arrival times at the fiber are randomly distributed. Each of the musculotendon actuators receives two input signals – a burst
signal analogous to alpha inputs and a conventional analogue signal that represents fusimotor input to the spindles. The process
of combining burst signals and conventional analogue signals is studied. Simulation results show that the movement of the
system with burst signals as inputs has overshoot and speed similar to the system with analogue signals.
Received: 30 May 1994/Accepted in revised form: 13 January 1995 相似文献
134.
Medicago truncatula (barrel medic) is an annual legume of agricultural and biological interest. In this report regeneration from isolated mesophyll protoplasts is described. A specifically developed, highly regenerable seed line is essential for regeneration. Other critical requirements for regeneration are the starting plant material, the use of agarose droplets incubated in a shallow layer of liquid medium, and protoplast density. Plants are grown in controlled environment conditions. Protoplasts are purified using a Percoll-based flotation procedure, then embedded in 100 l agarose droplets containing a basal medium plus 25 M NAA and 4 M BAP (the same medium as in the surrounding shallow liquid layer) to induce protoplast division. A protoplast density of 6–8×105 ml–1 is required for maximum colony formation. M. truncatula plants previously transformed for kanamycin resistance yielded embryogenic callus and also regenerated plants. Protoplasts from other annual Medicago (M.intertexta and M.scutellata) species readily form calli by the procedure we have described.Abbreviations BAP
6-benzylaminopurine
- 2,4-D
2,4-dichlorophenoxyacetic acid
- NAA
1-naphthaleneacetic acid 相似文献
135.
J D Schaeffer K J Kim E D Crandall 《Journal of applied physiology (Bethesda, Md. : 1985)》1984,56(1):72-77
The effects of decreased temperature, metabolic inhibition, and hyposmolality on osmotically and hydrostatically driven water flux across bullfrog alveolar epithelium were studied. Lungs were isolated from double-pithed Rana catesbeiana and prepared as sacs. Either an osmotic (0.1 M raffinose) or hydrostatic (6.3-6.6 Torr) pressure gradient was imposed across the tissue. These gradients resulted in the volume flow of water from the alveolar to pleural bath. Control water flux and hydraulic conductivity were estimated from the rate of weight loss of the lung sac. Subsequently water flux and hydraulic conductivity were determined under one of the following conditions: 1) temperature of bathing solutions lowered to 2 degrees C; 2) 1 mM 2,4-dinitrophenol added to both alveolar and pleural baths, or 3) both baths changed to half-isosmotic Ringer solution. The control hydraulic conductivities for osmotic (Lpo) and hydrostatic (Lph) pressure gradients were 3.65(+/- 0.94) X 10(-12) and 2.14(+/- 0.63) X 10(-10) ml/dyn X s, respectively. Under conditions of metabolic inhibition, hyposmolality, and decreased temperature, Lph decreased by 77, 83, and 92%, and Lpo decreased by 56, 34, and 59%, respectively. These results are most consistent with the hypothesis that the decrements in hydraulic conductivity under our experimental conditions are due to epithelial cell swelling and perhaps to changes in the characteristics of the paracellular pathway. 相似文献
136.
137.
Kim M. J.; Druz W. S.; Danon J.; Machnach W.; Sharp J. T. 《Journal of applied physiology》1978,45(3):392-398
138.
Cycloheximide at 0.1 to 0.2 m increases cAMP concentration up to five-fold in epididymal fat tissue . This increase in cAMP concentration is accompanied by a 40% activation of glycogen phosphorylase. Propranolol, a specific β-adrenergic antagonist, blocks the cycloheximide-mediated cAMP increase. Epinephrine stimulates cAMP formation up to 25-fold under the same condition. This increase is also blocked by propranolol. Cycloheximide also partially blocks the epinephrine stimulated cAMP increase, suggesting that both compounds act at the same site. 相似文献
139.
The presence of Ca2+-ATPase activities with high-affinity sites for Ca2+ in brush border as well as basolateral plasma membranes of rat duodenal epithelium has been reported previously (Ghijsen, W.E.J.M. and van Os, C.H. (1979) Nature 279, 802–803). Since both plasma membranes contain alkaline phosphatase (EC 3.1.3.1), which also can be stimulated by Ca2+, the substrate specificity of Ca2+-induced ATP-hydrolysis has been studied to determine whether or not alkaline phosphatase and Ca2+-ATPase are two distinct enzymes. In basolateral fragments, the rate of Ca2+-dependent ATP-hydrolysis was greater than that of ADP, AMP and at Ca2+ concentrations below 25 μM. At 0.2 mM Ca2+ the rates of ATP, ADP, AMP and hydrolysis were not significantly different. In brush border fragments the rates of ATP, ADP and AMP hydrolysis were identical at low Ca2+, but at 0.2 mM Ca2+, Ca2+-induced hydrolysis of ADP and AMP was greater than either ATP or . Alkaline phosphatase in brush border and basolateral membranes was inhibited by 75% after addition of 2.5 mM theophylline. Ca2+-stimulated ATP hydrolysis at 1 μM Ca2+ was not sensitive to theophylline in basolateral fragments while the same activity in brush border fragments was totally inhibited. At 0.2 mM Ca2+, Ca2+-induced ATP hydrolysis in both basolateral and brush border membranes was sensitive to theophylline. Oligomycin and azide had no effect on Ca2+-stimulated ATP hydrolysis, either at low or at high Ca2+ concentrations. Chlorpromazine fully inhibited Ca2+-stimulated ATP hydrolysis in basolateral fragments at 5 μM Ca2+, while it had no effect in brush border fragments. From these results we conclude that, (i) Ca2+-ATPase and alkaline phosphatase are two distinct enzymes, (ii) high-affinity Ca2+-ATPase is exclusively located in basolateral plasma membranes, (iii) alkaline phosphatase activity, present on both sides of duodenal epithelium, is stimulated slightly by low Ca2+ concentrations, but this Ca2+-induced activity is inhibited by theophylline and shows no specificity with respect to ATP, ADP or AMP. 相似文献
140.
The biogenesis of rat mitochondrial ATPase. Two subunits are synthesized inside the mitochondria 总被引:3,自引:0,他引:3
Isolated mitochondria from regenerating rat liver synthesize at least five different polypeptides with molecular weights ranging from 19 000 to 43 000. Among these, two polypeptides with molecular weights of 22 000 and 25 ooo could be identified as ATPase subunits. It has previously been shown that these subunits, designated 6 and 7, are lacking in the ATPase complex that is formed in vivo when mitochondrial protein synthesis is blocked by thiamphenicol treatment. The 22 000 Mr protein is enriched in the fraction containing the fully assembled ATPase complex, whereas the 25 000 Mr protein is not. 相似文献