全文获取类型
收费全文 | 40489篇 |
免费 | 3343篇 |
国内免费 | 3595篇 |
出版年
2024年 | 77篇 |
2023年 | 388篇 |
2022年 | 989篇 |
2021年 | 1744篇 |
2020年 | 1324篇 |
2019年 | 1592篇 |
2018年 | 1610篇 |
2017年 | 1216篇 |
2016年 | 1630篇 |
2015年 | 2385篇 |
2014年 | 2855篇 |
2013年 | 3137篇 |
2012年 | 3780篇 |
2011年 | 3445篇 |
2010年 | 2243篇 |
2009年 | 1980篇 |
2008年 | 2543篇 |
2007年 | 2182篇 |
2006年 | 1982篇 |
2005年 | 1693篇 |
2004年 | 1535篇 |
2003年 | 1415篇 |
2002年 | 1265篇 |
2001年 | 718篇 |
2000年 | 553篇 |
1999年 | 501篇 |
1998年 | 395篇 |
1997年 | 266篇 |
1996年 | 233篇 |
1995年 | 238篇 |
1994年 | 171篇 |
1993年 | 147篇 |
1992年 | 160篇 |
1991年 | 142篇 |
1990年 | 118篇 |
1989年 | 112篇 |
1988年 | 84篇 |
1987年 | 79篇 |
1986年 | 67篇 |
1985年 | 69篇 |
1984年 | 30篇 |
1983年 | 33篇 |
1982年 | 39篇 |
1981年 | 18篇 |
1979年 | 23篇 |
1978年 | 17篇 |
1977年 | 24篇 |
1976年 | 17篇 |
1975年 | 16篇 |
1972年 | 16篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
81.
Mu-Chin Tzeng Ming Jhy Hseu Jun Hai Yang Richard John Guillory 《The protein journal》1986,5(3):221-228
Snake presynaptic toxins such as crotoxin, β-bungarotoxin and taipoxin block neuromuscular transmission through inhibiting the release of acetylcholine by their phospholipase A2 activities. On the other hand, many other phospholipase A2s show little neurotoxicity. It is likely that the difference lies in whether high affinity binding to nerve cell membranes exists or not. To test this idea, crotoxin, β-bungarotoxin and taipoxin were first radioactively labeled with Na(125I) without loss of their neurotoxicity. Using the radioactive toxins we have found that each of the three showed specific binding to synaptosomal membranes from guinea pig brain. In contrast, we could not detect specific binding of a non-neurotoxic pancreatic phospholipase A2. Crotoxin and taipoxin, but not β-bungarotoxin, also bound specifically to membrane preparation from other tissues. The binding of each toxin was not greatly affected by the other two toxins. The photoaffinity labeling technique has been used to obtain further information about the components which bind crotoxin. For this purpose, (125I) crotoxin was derivatized with N-hydroxysuccinimidyl-4-azidobenzoate. Autoradiographic analysis of the membranes following photoirradiation in the presence of the modified crotoxin revealed that an 85K dalton component was preferentially covalently conjugated with the crotoxin analogue in a specific manner. 相似文献
82.
83.
苜蓿二磷酸核酮糖(RuBP)羧化酶体内活化作用的调节 总被引:6,自引:0,他引:6
苜蓿RuBP羧化酶的初活性和活化作用在不饱和光强下与光合速率一样随光强增加而增加。缺硫培养苜蓿叶片的光合速率和RuBP羧化酶的含量、初活性及总活性均比对照有不同程度的降低,其中酶的初活性与光合速率两者减少的趋势比较接近,说明RuBP羧化酶的初活性可能在光合CO_2固定作用中具有决定作用。然而,缺硫植株中酶的活化作用比对照明显增高。酶的活化作用与叶片中的叶绿素,6-PG,NADPH及ATP相对酶含量的比值成正比,与体内的酶量成反比。 相似文献
84.
Novobiocin blocks the Drosophila heat shock response 总被引:12,自引:0,他引:12
85.
We have previously shown that human subjects metabolize the 20 beta-epimer of isocortisol (11 beta, 17,20 beta-trihydroxy-3-oxo-pregn-4-en-21-al) to both 20 alpha- and 20 beta-hydroxy steroid end products. In this paper we describe the synthesis of tritium labeled 20 alpha-epimers of isocortisol and isoTHF (3 alpha, 11 beta, 17,20 alpha-tetrahydroxy-5 beta-pregnan-21-al) and their metabolic fate in humans. Both steroids yielded 20 alpha-hydroxy urinary neutral end-products (cortols and cortolones) and no 20 beta-hydroxy epimers. Regeneration of 17-ketols from aldols occurred to a small extent with isoTHF, but not with isocortisol. Isocortisol and isoTHF yielded less cortoic acids than did the corresponding ketols. The results provide further evidence that in man the stereochemistry at C-20 of the end-products of corticosteroid metabolism is determined by the configuration of the aldol at C-20 prior to subsequent metabolic events. 相似文献
86.
Intrathecal injection of subanalgesic doses of morphine (7.5 nmol) and dynorphin-A-(1–13) (1.25 nmol) in combination resulted in a marked analgesic effect as assessed by tail flick latency in the rat. The analgesic effect of the composite dynorphin/morphine was dose-dependent in serial dilutions so that a composition of 1/8 of the analgesic dose of dynorphin and 1/3 that of morphine produced an analgesic effect equipotent to full dose of either drug applied separately. The analgesic effect induced by dynorphin/morphine mixture was not accompanied by motor dysfunction and was easily reversed by a small dose (0.5 mg/kg) of naloxone. Contrary to the augmentatory effect of dynorphin on morphine analgesia in the spinal cord, intracerevroventricular (ICV) injection of 20 nmol of dynorphin-A-(1–13) exhibited a marked antagonistic effect on the analgesia produced by morphine (120 nmol, ICV). The theoretical considerations and practical implications of the differential interactions between dynorphin-A-(1–13) and morphine in the brain versus spinal cord are discussed. 相似文献
87.
Terry Joe Sprinkle F. Arthur McMorris Jun Yoshino George H. De Vries 《Neurochemical research》1985,10(7):919-931
The relative levels of the central nervous system myelin marker enzyme 2:3-cyclic nucleotide 3-phosphodiesterase (EC 3.1.4.37, CNPase) were determined in neuroblastoma, astrocyte, oligodendrocyte and Schwann cell cultures and in freshly isolated human lymphocytes and platelets. The highest specific activities were associated with the cells that elaborate myelin membrane in the central and peripheral nervous system, oligodendrocytes and Schwann cells, respectively. Antiserum to bovine CNPase recognized both CNP1 and CNP2 in CNS myelin and human oligodendroglioma. In addition, a 53,000 dalton protein was evident on autoradiographs of immunoblotted PNS myelin and human oligodendroglioma proteins. Cultured rat oligodendrocyte, C6 and mouse NA neuroblastoma CNPase appear to share common determinants with the corresponding normal rat CNS enzyme. 相似文献
88.
89.
90.
曾子申;胡峻;利容千 《武汉植物学研究》1985,3(4):439-442
本文对我国栽培辣椒Capsicum annuum L.的四个品种即汉川椒、华椒一号、牛角椒和二金条进行了核型分析,其染色体数目均为2n=2x=24,核型公式均为2n=24=20m+2sm+2st,但汉川椒和华椒一号具一对随体,牛角椒和二金条具两对随体。本文还对它们的进化关系进行了讨论。 相似文献