全文获取类型
收费全文 | 17754篇 |
免费 | 1473篇 |
国内免费 | 1438篇 |
出版年
2024年 | 46篇 |
2023年 | 226篇 |
2022年 | 490篇 |
2021年 | 729篇 |
2020年 | 551篇 |
2019年 | 679篇 |
2018年 | 745篇 |
2017年 | 615篇 |
2016年 | 855篇 |
2015年 | 1040篇 |
2014年 | 1243篇 |
2013年 | 1314篇 |
2012年 | 1535篇 |
2011年 | 1448篇 |
2010年 | 971篇 |
2009年 | 864篇 |
2008年 | 992篇 |
2007年 | 891篇 |
2006年 | 763篇 |
2005年 | 690篇 |
2004年 | 599篇 |
2003年 | 604篇 |
2002年 | 556篇 |
2001年 | 300篇 |
2000年 | 252篇 |
1999年 | 182篇 |
1998年 | 138篇 |
1997年 | 144篇 |
1996年 | 96篇 |
1995年 | 94篇 |
1994年 | 89篇 |
1993年 | 70篇 |
1992年 | 86篇 |
1991年 | 81篇 |
1990年 | 79篇 |
1989年 | 66篇 |
1988年 | 42篇 |
1987年 | 29篇 |
1986年 | 39篇 |
1985年 | 39篇 |
1984年 | 47篇 |
1983年 | 29篇 |
1982年 | 29篇 |
1981年 | 24篇 |
1980年 | 24篇 |
1979年 | 20篇 |
1978年 | 28篇 |
1977年 | 23篇 |
1976年 | 23篇 |
1973年 | 21篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
41.
42.
G. A. Romanov V. Ya. Taran L. Chvojka O. N. Kulaeva 《Journal of Plant Growth Regulation》1988,7(1):1-17
Purified fractions of soluble proteins from barley leaves have been shown to contain specific binding sites fortrans-zeatin, a natural cytokinin. Such binding is very strong in vitro in concentrated solutions of some salts (ammonium sulfate or potassium phosphate) with optimum at pH 7–8 and temperature within the range 0–20°C. The cytokinin-binding sites have high affinity for zeatin (Kd1.5·10–8 M) and low capacity corresponding to 1–1.5 pmol zeatin per milligram of initial soluble protein. Cytokinin binding is reversible; it is due to protein (or proteins) with molecular weight 40–45 kDa. This protein(s) does not bind3H-adenine and3H-abscisic acid. The ability of various compounds to displace3H-zeatin from its high-affinity binding sites is in strict accordance with their biological cytokinin activities. Other phytohormones as well as fusicoccin do not displace3H-zeatin from its binding sites. Specific zeatin binding is sensitive to heat, alkali, and pronase, but not to RNase treatment. The 150- to 200-fold purification of cytokinin-binding proteins was achieved by a combination of ammonium sulfate precipitation and Ultrogel AcA-54- and DEAE-cellulose chromatography. The zeatin-binding protein(s) from barley leaves is suggested to take part in cytokinin action in vivo. 相似文献
43.
不同季节银木叶精油化学成分的研究 总被引:1,自引:0,他引:1
黄远征;温鸣章;肖顺昌;赵蕙;任维俭 《武汉植物学研究》1988,6(3):253-259
用毛细管气相色谱-质谱-计算机联用技术、毛细管气相色谱双柱保留指数法和双柱标准品叠加法分析了不同季节银木叶精油化学成分。从分离出来的207—250个色谱峰中,初步鉴定出59个成分,被鉴定成分的总量占精油总组成的94.45—98.92%,其主要成分随采油季节不同而有所不同。 相似文献
44.
In enzymatically dissociated brain cells prepared from neonatal rats, KCl produced a significant increase in [Ca2+]i and this increase could be prevented by verapamil or nifedipine, known to block voltage-sensitive calcium channels. The opioid receptor agonists ohmefentanyl (OMF, mu agonist), [D-Pen2,D-Pen5]enkephalin (DPDPE, delta agonist), and 66A-078 (kappa agonist) produced a marked suppression of the Ca2+ influx induced by high K+ depolarization. The suppressive effect of OMF, DPDPE, and 66A-078 on the high K(+)-induced increase in [Ca2+]i was markedly reversed by their respective antagonists beta-funaltrexamine (beta-FNA), ICI174864, and nor-binaltorphimine (nor-BNI). Cholecystokinin octapeptide (CCK-8), at concentrations of 0.3, 3.0, and 30 nM, dose-dependently mobilized Ca2+ from intracellular stores. While CCK-8 30 nM did not affect significantly the increase of [Ca2+]i following high K+, it did reverse the suppression of the high K(+)-induced increase in [Ca2+]i by the mu agonist OMF and the kappa agonist 66A-078, but not that by the delta agonist DPDPE. The results suggested that while opioid ligands suppress [Ca2+]i by blocking voltage-operated Ca2+ influx, the antiopioid effect of CCK-8 seems to be operated via mobilization of Ca2+ from intracellular stores. 相似文献
45.
白腹锦鸡,红腹锦鸡,中国雉鸡SC组型的比较研究 总被引:1,自引:0,他引:1
以微铺展—硝酸银染色技术制备三种鸡的SC标本,进行电镜观察。结果表明:三种鸡的SC组非常相似,即2n=82,ZZ/ZW型性别决定,雄性为ZZ。除1号SC和Z-SC为中着丝粒外,其余均为端着丝粒。Z-SC的相对长度有明显的细胞间差异;平均相对长度度介于第3和第4号SC之间。三者SC组型上的差异主要表现在相应SC长度上的不同。并对其亲缘关系及在鸟类进化中的可能地位进行了讨论。此外,在微铺展法制备的锦鸡精母细胞SC标本中还发现了巨大中心粒,这在高等动物尚属首次。 相似文献
46.
P. Vuillez F. René M. Plante C. Hindelang M. J. Klein J. M. Félix M. E. Stoeckel 《Cell and tissue research》1992,267(1):169-183
Summary Organotypic cultures, in defined medium, of pituitary primordia obtained from 15-day-old rat fetuses were performed in order to study the in vitro differentiation of melanotrophic cells. The morphological and ultrastructural features of the transplants resembled those of the gland developing in vivo. In situ hybridization on semi-thin sections, using a 35S-labelled oligonucleotide probe, revealed pro-opiomelanocortin-mRNA-containing cells on the first day of culture in the anterior lobe and after 2–3 days in the intermediate lobe. Immunoperoxidase labelling of adjacent sections showed that the same cells reacted with antibodies against -melanocyte-stimulating hormone (MSH), 3 and adrenocorticotropic hormone in both lobes. The pro-opiomelanocortin-mRNA-containing cells formed progressively conspicuous areas in the intermediate lobe, which was almost uniformly labelled after 6 days. In the anterior lobe, these cells remained scattered in small cell groups, and colloidal gold immunolabelling showed the progressive disappearance of MSH labelling from the secretory vesicles in cells exhibiting morphological features of adult corticotrophic cells. Both the MSH content of the explants and MSH release into the culture medium increased with time. Treatment with the dopamine agonist bromocriptine induced a strong dose-dependent decrease in MSH secretion, which was significant after 3 days in culture, indicating that dopamine D2 receptors are able to regulate hormonal release of melanotrophic cells at early stages. This system constitutes a suitable model for further studies of factors controlling cell differentiation and cellular interactions involved in histogenesis. 相似文献
47.
A. A. Galoyan B. Ya. Gurvits L. A. Shuvalova Michael T. Davis John E. Shively Terry D. Lee 《Neurochemical research》1992,17(8):773-777
A new class of stimulators of basal activity of a number of calmodulin-dependent enzymes have been previously isolated from bovine hypothalamus. One of these stimulators, denoted as C3, has been purified to homogeneity by reverse phase HPLC and tentatively identified as thymosin 4 (1–39) by mass spectrometry and Edman microsequence analysis. The stimulating effect of C3 on rabbit skeletal muscle MLCK basal activity was compared with that of thymosin 1 and thymosin 4 (16–38). Evidence is presented that all the indicated compounds are Ca2+-independent high-affinity MLCK stimulators. The potency of the stimulators in activating the enzyme was: C3>4>(CaM+Ca2+>1.This revised version was published online in June 2005 with corrections to the author name Gurvits. 相似文献
48.
Roy E. Crabtree Edward C. Cyr Renée E. Bishop Laura M Falkenstein John M. Dean 《Environmental Biology of Fishes》1992,35(4):361-370
Synopsis Leptocephali were collected in June 1981 and July 1989 over the continental shelf and slope of the Florida west coast. Tarpon larvae ranged 5.5–24.4 mm standard length (SL) and were the second most abundant leptocephalus species. Sagittae examined with compound microscopes and scanning electron microscopy had increments that were presumed to be formed daily. Increment counts made using the two microscopic techniques were not significantly different. Estimated ages ranged 2–25 days with a growth rate (± standard error) of 0.92 ± 0.04 mm d–1 The least squares linear regression equation SL = 2.78 + 0.92 (age in days) best described the relationship between estimated age and length. Adult tarpon appear to undergo a substantial spawning migration from inshore areas frequented during spring and summer to offshore spawning grounds. Spawning occurs during May, June, and July, although the spawning season may be of greater duration. 相似文献
49.
Renmei Ren Kanhui Yan Yanjie Su Hanjun Qi Bin Liang Wunyong Bao Frans B. M. de Waal 《Primates; journal of primatology》1991,32(3):321-327
Observations were made following 130 spontaneous aggressive incidents in two small breeding groups of captive golden monkeys
(Rhinopithecus roxellanae roxellanae). Participants were observed both during the first 10 min following these incidents and during matched control observations.
An increased contact rate was observed between opponents following the aggressive incident. Post-conflict contacts were characterized
by a number of behavior patterns: open mouth, rapid grooming, embrace, and crouching. Adult males played an important role
as mediator in agonistic disputes among females: males intervened in 93.6% of female fights. It is speculated that this intervention
behavior is related to the species' organization into one-male units. 相似文献
50.
毒黄素对黄嘌呤氧化酶作用的影响 总被引:1,自引:0,他引:1
利用从椰毒假单胞菌(Pseudomona cocovenenans)中所分离提取的毒黄素(toxoflavin)对黄嘌呤氧化酶(EC.1、2 3、2)作用的动力学试验表明,毒黄素是此酶的非必需激活剂,而且对以次黄嘌呤为底物的反应的激活作用明显高于以黄嘌呤为底物的反应。此激活作用属于部分混合型。这一结果为探寻毒黄素对人体的致毒机理提供了一条重要线索。 相似文献