全文获取类型
收费全文 | 4401篇 |
免费 | 463篇 |
国内免费 | 1篇 |
出版年
2023年 | 19篇 |
2022年 | 34篇 |
2021年 | 74篇 |
2020年 | 61篇 |
2019年 | 70篇 |
2018年 | 79篇 |
2017年 | 56篇 |
2016年 | 124篇 |
2015年 | 184篇 |
2014年 | 195篇 |
2013年 | 235篇 |
2012年 | 318篇 |
2011年 | 313篇 |
2010年 | 170篇 |
2009年 | 184篇 |
2008年 | 248篇 |
2007年 | 224篇 |
2006年 | 235篇 |
2005年 | 215篇 |
2004年 | 237篇 |
2003年 | 210篇 |
2002年 | 219篇 |
2001年 | 52篇 |
2000年 | 41篇 |
1999年 | 61篇 |
1998年 | 76篇 |
1997年 | 50篇 |
1996年 | 50篇 |
1995年 | 55篇 |
1994年 | 37篇 |
1993年 | 50篇 |
1992年 | 36篇 |
1991年 | 36篇 |
1990年 | 46篇 |
1989年 | 36篇 |
1988年 | 30篇 |
1987年 | 39篇 |
1986年 | 22篇 |
1985年 | 28篇 |
1984年 | 36篇 |
1983年 | 39篇 |
1982年 | 36篇 |
1981年 | 33篇 |
1980年 | 18篇 |
1979年 | 19篇 |
1978年 | 18篇 |
1977年 | 25篇 |
1976年 | 26篇 |
1974年 | 17篇 |
1972年 | 15篇 |
排序方式: 共有4865条查询结果,搜索用时 46 毫秒
951.
Gildas Merceron Thomas M. Kaiser Dimitris S. Kostopoulos Ellen Schulz 《Proceedings. Biological sciences / The Royal Society》2010,277(1697):3105-3112
The successful evolutionary radiations of European hominoids and pliopithecoids came to an end during the Late Miocene. Using ruminant diets as environmental proxies, it becomes possible to detect variations in vegetation over time with the potential to explain fluctuations in primate diversity along a NW–SE European transect. Analysis shows that ruminants had diverse diets when primate diversity reached its peak, with more grazers in eastern Europe and more browsers farther west. After the drop in primate diversity, grazers accounted for a greater part of western and central European communities. Eastwards, the converse trend was evident with more browsing ruminants. These opposite trends indicate habitat loss and an increase in environmental uniformity that may have severely favoured the decline of primate diversity. 相似文献
952.
J.Michael Lord Lynne M. Roberts Philip E. Thorpe Ellen S. Vitetta 《Trends in biotechnology》1985,3(7):175-179
Many types of tumour cell express high levels of surface antigens which are largely absent from normal cells. Monoclonal antibodies against these surface antigens can be coupled to potent toxins to form conjugates (immunotoxins) which selectively kill the antigen-bearing cells. This article describes the components of immunotoxins, their modes of action and their clinical applications. 相似文献
953.
954.
Mark A. Yorek Joyce A. Dunlap Ellen M. Leeney Mark R. Stefani 《Journal of neurochemistry》1990,55(4):1366-1378
Aldose reductase activity is increased in neuroblastoma cells grown in media containing 30 mM fructose and/or 30 mM glucose. Neuroblastoma cells cultured in media supplemented with increased concentrations of glucose and fructose amass greater amounts of sorbitol than do cells exposed to media containing only high glucose concentrations. The increase in sorbitol content is dependent on the fructose and glucose concentration in the media. The increase in sorbitol content caused by exposing neuroblastoma cells to media containing 30 mM glucose/30 mM fructose is due to a protein synthesis sensitive mechanism and not to an alteration in the redox state. The addition of sorbinil to media containing 30 mM glucose blocks the increase in sorbitol content. In contrast, sorbinil treatment of media containing 30 mM glucose/30 mM fructose does not totally block the increase in sorbitol levels. myo-Inositol accumulation and incorporation into inositol phospholipids and intracellular myo-inositol content are decreased in cells chronically exposed to media containing 30 mM glucose or 30 mM glucose/30 mM fructose compared to cells cultured in unsupplemented media or media containing 30 mM fructose. However, maximal depletion of myo-inositol accumulation and intracellular content occurs earlier in cells exposed to media containing 30 mM glucose/30 mM fructose than in cells exposed to media supplemented with 30 mM glucose. Sorbinil treatment of media containing 30 mM glucose/30 mM fructose maintains cellular myo-inositol accumulation and incorporation into phospholipids at near normal levels. myo-Inositol content in neuroblastoma cells chronically exposed to media containing 30 mM glucose or 30 mM glucose/30 mM fructose recovers within 72 h when the cells are transferred to unsupplemented media or media containing 30 mM fructose. In contrast, the sorbitol content of cells previously exposed to media containing 30 mM glucose or 30 mM glucose/30 mM fructose then transferred into media containing 30 mM fructose remains elevated compared to the sorbitol content of cells transferred into unsupplemented media. These data suggest that fructose may be activating or increasing sorbinil-resistant aldose reductase activity as well as partially blocking sorbitol dehydrogenase activity. The presence of increased concentrations of fructose in combination with increased glucose levels may enhance alterations in cell metabolism and properties due to increased sorbitol levels. 相似文献
955.
Soluble dextran-ATP complexes have been synthesized using a bifunctional oxirane as the coupling agent. The degree of coupling is time-dependent, allowing materials of varying coenzyme loadings to be produced very simply. Characterization studies have shown that at the maximum coenzyme loading obtained (34 molecules per complex) all coenzyme moieties were coenzymically active with hexokinase. The extent of coenzyme loading was shown to have a considerable influence on the values of Km and Vmax of the complex as a substrate for hexokinase. Enzyme activity was also found with acetate kinase and myokinase, and coenzyme recycling (ATP, ADP) was demonstrated in an ultrafiltration reactor. 相似文献
956.
Cory Teuscher Suzanne M. Smith Ellen H. Goldberg Gene M. Shearer Kenneth S. K. Tung 《Immunogenetics》1985,22(4):323-333
Inbred strains of mice were studied for their susceptibility to the induction of experimental allergic orchitis after sensitization with mouse testicular homogenate in complete Freund's adjuvant accompanied by injections of extract from Bordetella pertussis. Susceptibility to autoimmune orchitis was found to be linked to the major histocompatibility complex in BALB/c and C57BL/10 mice and mapped to genes encoded within the H-2D
dregion. In five of six groups of bidirectional (susceptible × resistant) F1 hybrids, H-2D
d-linked susceptibility was inherited as a dominant autosomal trait. However, in (BALB/cByJ × DBA/2J)F1 and (DBA/2J × BALB/cByJ)F1 hybrids, dominant autosomal resistance to the induction of autoimmune orchitis was observed. Backcross analysis between the resistant F1 hybrid and the susceptible BALB/cByJ parent suggests that a single independently segregating DBA/2J locus is capable of negating H-2D
d-linked susceptibility, and controls resistance to the induction of autoimmune orchitis.Abbreviations used in this paper BP extract
Bordetella pertussis extract
- CFA
complete Freund's adjuvant
- EAO
experimental allergic orchitis
- Ir
immune response
- MHC
major histocompatibility complex
- MLH
mouse liver homogenate
- MTH
mouse testis homogenate
- PI
pathology index 相似文献
957.
Ornithine aminotransferase was purified by conventional biochemical methods from rat kidney, rat liver, and human liver. Affinity-purified antibodies raised to the rat kidney enzyme were used to produce an immunoadsorbent enabling a one-step purification of ornithine aminotransferase to be made from crude human liver extracts. The harsh chemical conditions often required to desorb immunoadsorbents were avoided by isolating antibodies with low functional affinity and employing an electrophoretic desorption method which allowed the enzyme activity to be retained. The close structural similarity between human and rat ornithine aminotransferase was demonstrated by immunodiffusion reactions. It was therefore possible to purify the enzyme from human liver using immobilized antibodies raised against rat kidney ornithine aminotransferase. Furthermore, desorption was more readily achieved due to the lower affinity for the human enzyme. 相似文献
958.
Consequences of increasing or decreasing plasma FSH concentrations during the preovulatory period in Romney ewes 总被引:2,自引:0,他引:2
K M Henderson L C Savage R L Ellen K Ball K P McNatty 《Journal of reproduction and fertility》1988,84(1):187-196
Romney ewes were infused with ovine FSH (NIADDK-oFSH-16) for 48 h from the initiation of luteolysis with cloprostenol. Doses of 2.5 or 5 micrograms/h which partly or completely prevented the normal preovulatory decline in plasma FSH concentrations caused a significant increase in mean ovulation rates. Ovulation rates were not increased significantly if the FSH (5 micrograms/h) was infused for only 20 h starting from the initiation of luteolysis or 24 h later. Infusion of a less potent and relatively impure preparation of FSH (i.e. FSH-P) at 0.5 mg/h for 48 h after cloprostenol treatment also increased the mean ovulation rate significantly. However, if the FSH-P was given for only the first 24 h, or if the start of the infusion was delayed for more than 12 h, mean ovulation rates were not increased significantly. Infusion of LH (NIADDK-oLH-25, 5 micrograms/h) for 48 h from the initiation of luteolysis decreased the mean ovulation rate significantly. Administration of bovine follicular fluid to suppress plasma FSH concentrations below normal during the first 24 h after cloprostenol injection did not delay oestrus. However, oestrus was delayed by approximately 2 days if plasma FSH concentrations were reduced by bovine follicular fluid 24 h after the initiation of luteolysis. As ovulation rate increased, the mean weight of individual corpora lutea of each ewe decreased. In ewes with a single ovulation, most corpora lutea weighed greater than 600 mg, but as the ovulation rate increased the proportion of corpora lutea present weighing less than 400 mg rose steadily.(ABSTRACT TRUNCATED AT 250 WORDS) 相似文献
959.
Zusammenfassung Eine Pilotstudie zur Auswilderung des Waldrapps wurde unter Berücksichtigung der Sozialstruktur durchgeführt. Da Waldrappe ihre Jungen bis zur nächsten Brutsaison führen, mußten zwei menschliche Pflegeeltern die Aufzucht- und Führungsrolle übernehmen. Sechs Jungvögel wurden zunächst von Hand aufgezogen und lange vor dem Flüggewerden an den Auflassungsort gebracht. Sie erhielten weitgehend natürliche Nahrung und wurden auch nach dem Ausfliegen von den beiden Pflegepersonen betreut. Somit wurde eine Familienstruktur geschaffen, die den Jungvögeln einerseits ein gefahrloses Erkunden ihrer Umwelt ermöglichte, andererseits eine zu große Zahmheit gegenüber Fremdpersonen verhinderte. In Feindmeidung, Nahrungssuch-Strategien und Nahrungwahl verhielten sie sich wie gleichaltrige Vögel aus Freilandpopulationen. Der positive Ausgang war Vorausbedingung für eine Auswilderung in Südspanien, die nach gleicher Methode ablaufen wird.
Successful introduction of Waldrapp Ibis (Geronticus eremita) on the basis of family bonding — a pilot study in Austria
Summary In 1991, the Alpenzoo Innsbruck/Tirol initiated a pilot study to test a new method for releasing the highly endangered Waldrapp Ibis into its natural habitat based on the complex social system and tight family bonds of this highly social species. Young Waldrapp Ibises have a very close contact with their parents, usually up to the next breeding season. Especially in the first fledgling days the guidance of the parents is indispensable. Six chicks of the colony in the Alpenzoo were handreared to produce parent imprinting. In order to achieve food imprinting the birds were fed to a large extend on insects wich constitute their natural food. Handrearing took place at the releasing station, an adapted farmhouse near Innsbruck. Two human foster parents stayed continuously with the fledglings for six month. The simulated family structure enabled the young birds to get familiar with the habitat and to learn foraging whilst enjoying permanent protection. Being guided by only two persons the birds did not become too tame; they ignored other people and learned to avoid dangerous man made situations (e.g. cars, roads, dogs). The ability of our birds to orientate, their feeding behaviour, choice of food and use of habitat were identical to what is known of Waldrapp Ibises of the same age living in the wild, for example in the colonies in Morocco. The successful pilot study is considered to be the basis for a releasing program intended in a protected area of southern Spain.相似文献
960.