全文获取类型
收费全文 | 15415篇 |
免费 | 892篇 |
国内免费 | 6篇 |
出版年
2022年 | 66篇 |
2021年 | 153篇 |
2020年 | 95篇 |
2019年 | 132篇 |
2018年 | 177篇 |
2017年 | 170篇 |
2016年 | 281篇 |
2015年 | 454篇 |
2014年 | 531篇 |
2013年 | 1033篇 |
2012年 | 962篇 |
2011年 | 966篇 |
2010年 | 609篇 |
2009年 | 573篇 |
2008年 | 963篇 |
2007年 | 1020篇 |
2006年 | 890篇 |
2005年 | 936篇 |
2004年 | 913篇 |
2003年 | 839篇 |
2002年 | 827篇 |
2001年 | 228篇 |
2000年 | 221篇 |
1999年 | 260篇 |
1998年 | 234篇 |
1997年 | 166篇 |
1996年 | 147篇 |
1995年 | 129篇 |
1994年 | 122篇 |
1993年 | 133篇 |
1992年 | 169篇 |
1991年 | 139篇 |
1990年 | 133篇 |
1989年 | 153篇 |
1988年 | 93篇 |
1987年 | 113篇 |
1986年 | 105篇 |
1985年 | 117篇 |
1984年 | 121篇 |
1983年 | 81篇 |
1982年 | 98篇 |
1981年 | 79篇 |
1980年 | 72篇 |
1979年 | 64篇 |
1978年 | 52篇 |
1977年 | 65篇 |
1976年 | 54篇 |
1975年 | 58篇 |
1974年 | 40篇 |
1973年 | 46篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
21.
T Nimura M Okada M Shimizu M Kawabe T Itoh M Iwasaki H Kimura T Takeuchi 《The Annals of physiological anthropology》1990,9(4):329-333
Motorcyclists who work in some offices sometimes complained of coldness, pain and numbness of upper limbs. We studied how to discriminate between vibration syndrome and local fatigue of the motorcyclists. Subjects are 42 motorcyclists of an office in Aichi prefecture. 25 of them held several letters in their left hand when they delivered the letters. They complained of coldness, pain and numbness in the left upper limbs more than in the right limbs (p less than 0.01). We think that it is the local fatigue rather than the disorder of vibration syndrome that causes such symptoms. So it is very important to recognize the existence of local fatigue in order to know how to discriminate between vibration syndrome and local fatigue of the motorcyclists. 相似文献
22.
23.
24.
25.
We separated two forms of arylalkylamine N-acetyltransferase (AANAT) from various organs of the American cockroach, Periplaneta americana. Both forms of the enzyme had an equivalent molecular mass of 28 kDa. One form isolated from the testicular accessory glands had high enzyme activity at acidic pHs. The isoelectric point was 5-6 and the substrate specificity was wider than the other type. The other isolated form from female midguts had a higher level of enzyme activity at basic pHs. These findings suggested that P. americana contains polymorphic AANAT, as is the case in Drosophila melanogaster. These forms differed not only in pH specificity, and substrate specificity but in chromatographic behavior and kinetic properties. Most of the organs we examined contained a mixture of the two forms since two types of AANAT activity were separated in different chromatographic fractions when two pH conditions were used for activity measurement. 相似文献
26.
The rate constant of modification of a specific thiol group, SH2, with N-ethylmaleimide (NEM) has been used to estimate the conformational change in the local area containing SH2 (SH2 region) of skeletal myosin as a structural probe. The rate of Mg2+-ATP-induced SH2 modification of subfragment-1 (S-l) isozymes was regulated by Ca2+ in the pCa range below 6.4 and was not regulated in the pCa range above 6.4. No substantial difference between S-1 containing alkali light chain, A1, (S-1(A1)) and S-1 containing alkali light chain, A2, (S-1(A2)) was observed in the Ca2+-dependent rate of SH2 modification. Due to the presence of this Ca2+ regulation in myosin (absence in S-1 isozymes) in the pCa range above 6.4, absence of 5,5-dithiobis-(2-nitrobenzoic acid) (DTNB) light chain in S-1 isozymes, and high affinity of Ca2+ for DTNB light chain, this Ca2+ regulation in the pCa range above 6.4 is possibly related to the Ca2+ binding to DTNB light chain. F-Actin, which is entirely free from tropomyosin and troponin, enhanced the rate of Mg2+-ATP-induced SH2 modification of S-1 isozymes equally and of myosin, and reduced the Ca2+ sensitivity with an increase in F-actin concentration. 相似文献
27.
Takashi Yamashita Naoto Tonouchi Takeshi Uozumi Teruhiko Beppu 《Molecular & general genetics : MGG》1987,210(3):462-467
Summary The aspartic protease gene of a zygomycete fungus Mucor pusillus was expressed in Saccharomyces cerevisiae under the control of the yeast GAL7 promoter. A putative preproenzyme with an NH2-terminal extension of 66 amino acids directed by the gene was processed in yeast cells and the mature enzyme, whose NH2-terminus was identical to that of the Mucor enzyme, was efficiently secreted into the medium at a concentration exceeding 150 mg/l. The enzyme secreted from the recombinant yeast was more glycosylated than the native Mucor enzyme but its enzymatic properties were almost identical with those of the native enzyme, which has been used as a milk coagulant in cheese manufacture. 相似文献
28.
The catalase molecule in germinating pumpkin cotyledons is synthesizedas a precursor (59-kDa) form, whose relative molecular massis larger than the mature enzyme (55-kDa). Although both typesof molecules are localized in the microbodies, the 59-kDa specieshas been shown to be present predominantly in the leaf peroxisomesisolated from green cotyledons, while the 55-kDa species ispredominantly in the glyoxysomes from etiolated cotyledons [Yamaguchiet al. (1984) Proc. Natl. Acad. Sci. USA, 81: 4809]. We examinedthe distribution of the 59- and 55-kDa catalase molecules indark- and light-grown tissues of pumpkin seedlings as well asin other plant species, using the immunoblotting technique.The ratios of the 59- and 55-kDa catalase species differed inthe pumpkin tissues examined. Light interferes with the conversionof the 59-kDa precursor to the 55-kDa form, especially in thecotyledons. The effect of light was less pronounced in the rootsand hypocotyls, indicating that the light regulation of theconversion is tissue-specific. Dark- and light-grown cotyledonsfrom cucumber and watermelon seedlings showed a similar lightregulation, suggesting that cucurbitaceous plants possess similarlight-regulatory mechanism. From the analysis of catalase proteinfrom various plant tissues, a limited correlation between molecularforms of catalase and different microbody populations was observed. (Received September 6, 1986; Accepted December 4, 1986) 相似文献
29.
Induction and subsequent repair of DNA damage by fast neutrons in cultured mammalian cells 总被引:1,自引:0,他引:1
The induction and repair of DNA damage were studied by a DNA unwinding method in mouse L5178Y cells exposed to fast neutrons. DNA lesions induced by fast neutrons were classified into three types from their repair profiles: fast-reparable breaks (T1/2 = 3-5 min), slow-reparable breaks (T1/2 = 70 min), and nonreparable breaks. The repair rates of both fast-reparable and slow-reparable breaks were almost the same as those of corresponding damage induced by low-LET radiation. Neutrons induced a smaller amount of fast-reparable damage, an almost equal amount of slow-reparable damage, and a larger amount of nonreparable damage than those induced by equal doses of gamma rays or X rays. RBEs for fast- and slow-reparable damage were 0.3 and 0.9, respectively. The RBE for nonreparable damage was dose dependent and was 1.4 at the level of 100 breaks/10(12) Da DNA. Among the three types of lesions, only the nonreparable damage levels correlated with the linear-quadratic shape of the survival curves and with the enhanced killing effectiveness of neutrons (RBE = 1.7 at D0). 相似文献
30.
A glycine-rich antibacterial protein with a molecular mass of 7,000 termed sarcotoxin III, was purified to homogeneity from the hemolymph of third instar larvae of Sarcophaga peregrina. When the hemolymph was fractionated, this protein was recovered in the same fraction as sarcotoxin I, a group of potent antibacterial proteins that have been purified. But, it was clearly different from sarcotoxin I in amino acid composition and molecular mass. Sarcotoxin III was shown to be induced in the hemolymph in response to injury of the larval body wall. 相似文献