全文获取类型
收费全文 | 44657篇 |
免费 | 3639篇 |
国内免费 | 4篇 |
出版年
2023年 | 224篇 |
2021年 | 328篇 |
2020年 | 300篇 |
2019年 | 289篇 |
2018年 | 891篇 |
2017年 | 923篇 |
2016年 | 969篇 |
2015年 | 802篇 |
2014年 | 956篇 |
2013年 | 1788篇 |
2012年 | 3046篇 |
2011年 | 3447篇 |
2010年 | 1736篇 |
2009年 | 1122篇 |
2008年 | 2836篇 |
2007年 | 2908篇 |
2006年 | 2709篇 |
2005年 | 2420篇 |
2004年 | 2323篇 |
2003年 | 2177篇 |
2002年 | 2171篇 |
2001年 | 1499篇 |
2000年 | 1739篇 |
1999年 | 915篇 |
1998年 | 437篇 |
1997年 | 347篇 |
1996年 | 419篇 |
1995年 | 367篇 |
1994年 | 386篇 |
1993年 | 361篇 |
1992年 | 368篇 |
1991年 | 314篇 |
1990年 | 274篇 |
1989年 | 254篇 |
1988年 | 243篇 |
1987年 | 257篇 |
1986年 | 216篇 |
1985年 | 303篇 |
1984年 | 363篇 |
1983年 | 331篇 |
1982年 | 313篇 |
1981年 | 296篇 |
1980年 | 262篇 |
1979年 | 265篇 |
1978年 | 260篇 |
1977年 | 244篇 |
1976年 | 240篇 |
1975年 | 284篇 |
1974年 | 211篇 |
1973年 | 196篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
951.
Helmut Hölder 《Pal?ontologische Zeitschrift》1978,52(3-4):280-304
The Parapatocerates from the Süntel (Weser mountains, Northwest Germany) are described being an utmost variable subspecies respectively geographical raceParapatoceras distans (?) bentzi (Potonié) with two possibly modificatorily separated form groups. They differ from the similarP. distans(?) crioconus (Buckman) (=Crioconites Buckman) of Chippenham (England) in primary quadrilobaty and further characteristics accessible only by precise analysis. To establish the speciesdistans Baugier & Sauzé and with this the genusParapatoceras, recovery of the holotype or a determination of a neotype is required. A very similar but probably quinquelobate specimen (Parapatoceras sp.) from the Macrocephalus oolite of Hanover seems to accentuate once more the taxonomically minor degree of the quadri- or quinquelobaty inParapatoceras. 相似文献
952.
Light-induced fluorescence decay was examined during the greening of control and lincomycintreated maize (Zea mays L.) leaves. Assuming that this decay to a first approximation is the result of two parallel first-order reactions, the fluorescence induction curves were linearized on the logarithm plot and the parameters were determined. The variable fluorescence increased, and the parameters of the two linear sections of the fluorescence decay—that is, the kinetics of the induction curves—changed during the greening of the control leaves. Lincomycin treatment caused some chlorophyll deficiency and the lowering of the chlorophyll a/b ratio, changed the fluorescence emission spectra and the effect of Mg2+ on the regulation of the excitation energy distribution. The structure of the thylakoids and the kinetics of the fluorescence decay were also changed in the treated leaves. The possible relationship between the change of the kinetics of the fluorescence decay and the change of spillover during greening and after lincomycin treatment is discussed.Abbreviations LHC
light-harvesting complex
- Chl
chlorophyll
- LM
lincomycin
- PS
photosystem
- DCMU
3-(3,4-dichlorophenyl)-1,1-dimethylurea 相似文献
953.
Protoplasts from Chlamydomonas smithii prepared by the action of C. reinhardii gamete autolysine have been studied with respect to cell wall regeneration. Natural protoplasts within sporangia were also investigated for purposes of comparison. In both cases a new cell wall is completed within 2–3 h of the onset of regeneration. The first visible stages of wall regeneration are to be seen after 40–60 min as a fine fringe outside of the plasmalemma. The development of the typical central triplet follows within the next 1 h. Cell wall regeneration is reversibly inhibited by cycloheximide (10g ml-1) and reversibly disturbed by concanavalin A (50 g ml-1). Actinomycin D at concentration over 100g ml-1 also inhibit but the inhibition is irreversible and peculiar membrane effects are observed. Chelators (ethylenediamine tetraacetic acid; ethyleneglycol-bis-aminoethyl ether) and 2-deoxyglucose slightly retard or have no effect on cell wall regeneration.Abbreviations EDTA
ethylenediamine tetraacetic acid
- EGTA
ethyleneglycol-bis(aminoethyl ether)
- N,N
tetraacetic acid 相似文献
954.
O. H. Spieser J. H. Schröder 《TAG. Theoretical and applied genetics. Theoretische und angewandte Genetik》1978,51(5):223-232
Summary An inbred strain (Istanbul) of guppies was divided into two substrains, one of which was maintained and bred in seawater. The offspring of irradiated animals of both substrains (1000 R X-rays to spermatogonia and oogonia of neonatal fish) were tested in a new gruppy male courtship activity test and compared with control groups. The postirradiation response in the seawater substrain was more intense than in the freshwater substrain.Dedicated to Prof.Dr.Dr.h.c.mult. Curt Kosswig on the occasion of his 75th birthday 相似文献
955.
956.
Otto E. Rössler 《Bulletin of mathematical biology》1978,40(1):45-58
For certain environments, the Darwinian model allows unique prediction of a function that any surviving system adapted to
such an environment has to perform. This is the case for those environments that determine a “survival functional” of position
in space-time of known shape. Purely temporal survival functionals can be distinguished from spatial and mixed ones. In each
case, there exists an optimum path in combined physical and (reduced) metabolic space. Dependent on the admissible error,
approximate solutions of different complexity are sufficient. All solutions possess an afferent, a central, and an efferent
part. Within this general frame, specific, “probably simplest”, solutions are proposed for adaptive chemotaxis, insect locomotion,
lower vertebrates locomotion, higher vertebrates locomotion, chronobiological systems, and immune systems, respectively—or
rather, for the underlying functionals.
Presented at the Society for Mathematical Biology Meeting, University of Pennsylvania, Philadelphia, August 19–21, 1976. 相似文献
957.
Oxidation of ferrocytochrome c by molecular oxygen catalysed by cytochrome c oxidase (cytochrome aa3) is coupled to translocation of H+ ions across the mitochondrial membrane. The proton pump is an intrinsic property of the cytochrome c oxidase complex as revealed by studies with phospholipid vesicles inlayed with the purified enzyme. As the conformation of cytochrome aa3 is specifically sensitive to the electrochemical proton gradient across the mitochondrial membrane, it is likely that redox energy is primarily conserved as a conformational “strain” in the cytochrome aa3 complex, followed by relaxation linked to proton translocation. Similar principles of energy conservation and transduction may apply on other respiratory chain complexes and on mitochondrial ATP synthase. 相似文献
958.
959.
960.
Muramyl dipeptide (MDP), a synthetic adjuvant, increased the primary response of CBA mice to sheep red blood cells (SRBC). In reconstituted irradiated recipients, cooperation between T and B lymphocytes was required for the expression of adjuvant activity and MDP increased the efficiency of SRBC-educated T cells. The role of T-derived lymphocytes in mediating the MDP adjuvant activity was also demonstrated in irradiated mice and in mice reconstituted with various splenic cellular types of donors which had received SRBC and MDP 24 hr earlier. In our experiments, the macrophage did not seem to be involved, since MDP did not increase the phagocytic capacity of peritoneal exudate cells and MDP- and SRBC-pretreated macrophages had no increased ability to induce an anti-SRBC immune response. These results demonstrate the importance of T lymphocytes as mediators of the adjuvant activity of MDP. 相似文献