全文获取类型
收费全文 | 3727篇 |
免费 | 202篇 |
国内免费 | 1篇 |
出版年
2021年 | 30篇 |
2019年 | 23篇 |
2018年 | 43篇 |
2017年 | 32篇 |
2016年 | 54篇 |
2015年 | 60篇 |
2014年 | 98篇 |
2013年 | 350篇 |
2012年 | 176篇 |
2011年 | 164篇 |
2010年 | 105篇 |
2009年 | 111篇 |
2008年 | 184篇 |
2007年 | 189篇 |
2006年 | 193篇 |
2005年 | 176篇 |
2004年 | 170篇 |
2003年 | 180篇 |
2002年 | 192篇 |
2001年 | 82篇 |
2000年 | 71篇 |
1999年 | 83篇 |
1998年 | 68篇 |
1997年 | 46篇 |
1996年 | 35篇 |
1995年 | 40篇 |
1994年 | 32篇 |
1993年 | 44篇 |
1992年 | 56篇 |
1991年 | 60篇 |
1990年 | 49篇 |
1989年 | 48篇 |
1988年 | 33篇 |
1987年 | 37篇 |
1986年 | 33篇 |
1985年 | 42篇 |
1984年 | 47篇 |
1983年 | 45篇 |
1982年 | 36篇 |
1981年 | 45篇 |
1980年 | 33篇 |
1979年 | 41篇 |
1978年 | 38篇 |
1977年 | 21篇 |
1976年 | 22篇 |
1974年 | 25篇 |
1973年 | 19篇 |
1972年 | 25篇 |
1968年 | 18篇 |
1967年 | 18篇 |
排序方式: 共有3930条查询结果,搜索用时 171 毫秒
101.
Roles of auxin and gibberellic acid in growth and maturation of epicotyls of Vigna angularis: Cell wall changes 总被引:1,自引:0,他引:1
The effects of auxin and gibberellic acid on cell wall composition in various regions of epicotyls of azuki bean ( Vigna angularis Ohwi and Ohashi cv. Takara) were investigated with the following results. (1) Young segments excised from apical regions of the epicotyl elongated in response to added 10−4 M indole-3-acetic acid (IAA). When the segments were supplied with 50 m M sucrose, the IAA-induced segment growth was accompanied by enhanced overall synthesis of cell wall polysaccharides, such as xyloglucans, polyuronides and cellulose. This IAA effect on the cell wall synthesis is a consequence of extension growth induced by IAA. Gibberellic acid (GA) at 10−4 M synergistically enhanced the IAA-induced cell wall synthesis as well as IAA-induced extension growth, although GA by itself neither stimulated the cell wall synthesis nor extension growth. In the absence of sucrose, cell wall synthesis was not induced by IAA or GA. (2) In mature segments excised from basal regions of the epicotyl, no extension growth was induced by IAA or GA. GA enhanced the synthesis of xylans and cellulose when the segments were supplied with 50 m M sucrose. IAA had no effect on the cell wall synthesis. These findings indicate that synthesis of polyuronides, xyloglucans and cellulose, which occurs during extension growth of the apical region of the epicotyl, is regulated chiefly by auxin whereas synthesis of xylans and cellulose during cell maturation in the basal region of the epicotyl is regulated by GA. 相似文献
102.
Satoru Kawamura Tôru Yoshizawa Kazumi Horiuchi Masayoshi Ito Akiko Kodama Kiyoshi Tsukida 《BBA》1979,548(1):147-152
9-cis-Retro-γ;rhodopsin (λmax = 420 nm) was prepared from 9-cis-retro-γ-retinal and cattle opsin. After cooling to liquid nitrogen temperature (77 K), the pigment was irradiated with light at 380 nm. The spectrum shifted to the longer wavelengths, owing to formation of a batho product. This fact indicates that the conjugated double bond system from C-5 to C-8 of the chromophoric retinal in rhodopsin was not necessary for formation of bathorhodopsin. Reirradiation of the batho product with light at wavelengths longer than 520 nm yielded a mixture composed of presumably 9- or 11-cis forms of retro-γ-rhodopsin. These three isomers are interconvertible by light at liquid nitrogen temperature. Thus the retro-γ-rhodopsin system is similar in photochemical reaction at 77 K to cattle rhodopsin system. Each system has its own batho product. Based on these results, it was infered that the formation of bathorhodopsin is due to photoisomerization of the chromophoric retinal of rhodopsin and is not due to translocation of a proton on the ring or on the side chain from C-6 to C-8 of the chromophoric retinal to the Schiff-base nitrogen. 相似文献
103.
Summary
Allium sativum L. (2 n=16) had three types of clones with regard to the number of chromosomes carrying well-defined secondary constrictions: the first type had two secondary constricted chromosomes (type I), the second had three (type II) and the third had four (type III). Silver staining was applied to these three types of cells to determine the number of nucleolus organizing regions (NORs) per cell and to study the relationship between the morphological appearance of the secondary constrictions and the ability of the chromosomes to form nucleoli. Ag-positive regions appeared on two chromosomes in type I, on three in type II and on four in type III. The comparison of Giemsa and Feulgen stained chromosomes with the silver stained ones clearly indicated that the positive reaction with silver occurred exclusively on the secondary constricted regions that responded negatively to both Giemsa and Feulgen staining, indicating that the size of the achromatic secondary constrictions directly reflects the volume of the Ag-positive materials. However, all three types of clones had a maximum of four nucleoli at interphase. Of the four nucleoli, either two or one was extremely small (less than 1 m in diameter) in types I and II respectively. The size variations of the other nucleoli seemed to be positively correlated with those of the Ag-positive regions. This and the observation that the maximum number of nucleoli per cell did not coincide with the number of Ag-positive regions on the metaphase chromosome complement suggest strongly that the NORs responsible for the minute nucleoli cannot be detected on the metaphase chromosomes. The present observations indicate that not all NORs are indicated by the morphological appearance of secondary constrictions. 相似文献
104.
Yoshizawa Itsuo Nagata Kyoko Ohuchi Ryoko Itoh Shinji Kanaiwa Yoshio Amiya Takashi 《Steroids》1980,36(1):87-96
Two D-homosteroids were isolated from the hydrolyzate of 5β-pregnane -3α,20α-diol disulfate (II) when it was refluxed in 3N hydrochloric acid. The structures of these steroids have been elucidated as 17α-methyl-D-homo-5β-androstane-3α, 17aβ-diol (VI) and 17α-methyl-17aγb-chloro-D-homo-5β-androstan-3α-ol (VIII) by instrumental analyses. The former was identical with a synthetic specimen derived from 5β-pregnane-3α,20β-diol di-sulfate (IV) by uranediol rearrangement. The main hydrolyzates obtained were 17α-ethyl-17β-methyl-18-nor-5β-androst-13-en-3α-ol (V) and 5β-pregnane-3α, 20α-diol (III). 相似文献
105.
Yoshio Honma Keizo Takenaga Takashi Kasukabe Motoo Hozumi 《Biochemical and biophysical research communications》1980,95(2):507-512
Human promyelocytic leukemia cells (HL-60) were induced to phagocytize, reduce NBT dye(nitroblue tetrazolium), and change into forms that were morphologically similar to mature granulocytes by retinoic acid and related retinoids, but not by the pyridyl analog of retinoic acid. Induction of differentiation could be detected after 4 days of treatment of the cells with retinoic acid at as low a dose as 4 × 10?8 M. Thus, retinoids may be used in studies on the control of cell differentiation and malignancy of human myeloid leukemia cells. 相似文献
106.
107.
Measurement of endogenous growth rates and the mechanical propertyof the cell wall in various regions of light-grown azuki beanepicotyls revealed diat the minimum stress-relaxation time (To)was the shortest in the upper region (030 mm below theapex) of the epicotyl, where vigorous endogenous growth tookplace, and became longer toward the basal region, which wasmature and not growing. In the upper region of the epicotyl, a lower percentage of a-celluloseand a higher percentage of pectic substances than in the lowerregion were found. The percentage of hemicellulose content wasalmost constant over the whole epicotyl. Major components ofnoncellulosic neutral sugars in the cell wall were galactoseand xylose. The percentage of the galactose content to the noncellulosicpolysaccharide was highest in the upper region and lowest inthe basal region of the epicotyl, and a clearly negative correlationbetween the galactose composition and the To value was obtained.On the contrary, the percentage of die xylose content was highestin the basal region and lowest in die upper region, and a clearlypositive correlation between die xylose composition and theTo value was obtained. During die endogenous growth of die intactepicotyl, all die neutral sugars, particularly galactose, increasedin die upper region, whereas in die middle and basal regions,only xylose increased. Similar changes in sugar compositionswere observed during IAA-induced elongation of die segment excisedfrom various regions of die epicotyl. (Received July 27, 1978; ) 相似文献
108.
Quantitative study of the cytochrome c acting in the photosyntheticsystem of the blue-green alga Anabaena variabilis (M-2) wasdone with membrane fragments and intact cells. Membrane fragments highly active in the NADP+-Hill reaction(above 200 µmoles/mg chl.a;-hr) retained photoresponsivecytochrome c equal only one-tenth that of P700, while the plastocyanincontent was almost equal to that of P700. The cytochrome contentin intact cells was a little larger than that in membrane fragmentson the chlorophyll a basis. However, the values relative toP700 (1/9) and plastocyanin (1/10) were identical with thosein membrane fragments. The content was also far smaller thanthat of reaction center II's (1/6). If the cytochrome mediatesall electrons from reaction center II, the cytochrome oxidation-reductionshould have a rate constant of 2.4?102 sec1 which isone order above of the rate constant of the cytochrome reduction(2.3 to 3.5?101sec1). These quantitative relationshipsindicate that in Anabaena variabilis (M-2), c-type cytochrome,either cytochrome f or algal cytochrome c, cannot function inthe main electron flow between two reaction centers. (Received September 8, 1978; ) 相似文献
109.
Changes in cell wall polysaccharides and mechanical propertiesof the cell wall were examined during IAA-induced elongationgrowth of excised azuki bean epicotyl segments under differentgrowth conditions. Sucrose promoted IAA-induced cell elongation,but had very little effect on IAA-induced cell wall loosening.In the absence of sucrose, the amount of galactose in the cellwall decreased during the incubation period. IAA enhanced thedecrease in the galactose level. In the presence of sucrose,on the other hand, IAA induced increases in the amounts of cellulose,galactose and xylose in noncellulosic polysaccharides. TheseIAA-induced increases were not observed in the presence of mannitolat concentrations higher than 0.1 M, although cell wall looseningwas induced by IAA even in the presence of 0.2 M mannitol. (Received November 21, 1978; ) 相似文献
110.
Summary Glucose oxidase (GOD) was immobilized on a nylon membrane. No activity of the GOD-nylon membrane was observed under normal
conditions but it appeared when the membrane was mechanically stretched. A linear relationship was observed between the stress
strength and the GOD activity of the membrane. The appearance of the GOD activity of the membrane with stress was reproducible
and the membrane could be stored for at least 2 months. Therefore, the GOD-nylon membrane can be called a stress sensitive
membrane. 相似文献