全文获取类型
收费全文 | 126篇 |
免费 | 19篇 |
国内免费 | 17篇 |
出版年
2023年 | 3篇 |
2022年 | 2篇 |
2021年 | 6篇 |
2020年 | 3篇 |
2019年 | 1篇 |
2017年 | 1篇 |
2016年 | 5篇 |
2015年 | 4篇 |
2014年 | 6篇 |
2013年 | 6篇 |
2012年 | 11篇 |
2011年 | 8篇 |
2010年 | 9篇 |
2009年 | 11篇 |
2008年 | 5篇 |
2007年 | 9篇 |
2006年 | 5篇 |
2005年 | 10篇 |
2004年 | 2篇 |
2003年 | 6篇 |
2002年 | 3篇 |
2001年 | 5篇 |
2000年 | 6篇 |
1999年 | 4篇 |
1998年 | 7篇 |
1997年 | 3篇 |
1996年 | 2篇 |
1995年 | 1篇 |
1994年 | 1篇 |
1993年 | 2篇 |
1989年 | 1篇 |
1988年 | 1篇 |
1987年 | 1篇 |
1986年 | 1篇 |
1983年 | 1篇 |
1982年 | 1篇 |
1981年 | 1篇 |
1978年 | 1篇 |
1977年 | 4篇 |
1976年 | 2篇 |
1966年 | 1篇 |
排序方式: 共有162条查询结果,搜索用时 15 毫秒
131.
132.
133.
134.
A positive family history of alcohol use disorders (FH) is a robust predictor of personal alcohol abuse and dependence. Exposure to problem-drinking models is one mechanism through which family history influences alcohol-related cognitions and drinking patterns. Similarly, exposure to alcohol advertisements is associated with alcohol involvement and the relationship between affective response to alcohol cues and drinking behavior has not been well established. In addition, the collective contribution that FH, exposure to different types of problem-drinking models (e.g. parents, peers) and personal alcohol use have on appraisal of alcohol-related stimuli has not been evaluated with a large sample. We investigated the independent effects of FH, exposure to problem-drinking models and personal alcohol use on valence ratings of alcohol pictures in a college sample. College students (n = 227) completed measures of personal drinking and substance use, exposure to problem-drinking models, FH and ratings on affective valence of 60 alcohol pictures. Greater exposure to non-familial problem-drinkers predicted greater drinking among college students (beta = 0.17, P < 0.01). However, personal drinking was the only predictor of valence ratings of alcohol pictures (beta = -0.53, P < 0.001). Personal drinking level predicted valence ratings of alcohol cues over and above FH, exposure to problem-drinking models and demographic characteristics. This suggests that positive affective responses to alcohol pictures are more a function of personal experience (i.e. repeated heavy alcohol use) than vicarious learning. 相似文献
135.
目的研究高纯度大豆卵磷脂对中国仓鼠肺细胞(cHL)染色体畸变作用。方法测定高纯度大豆卵磷脂对CHL细胞的半数抑制浓度(IC50),根据IC50设立不同剂量组,进行正式试验,分别观察高纯度大豆卵磷脂接触CHL6h,24h及加S9后6h染色体的畸变情况,根据标准进行结果判定。结果染毒6h,24h及加S9后染毒6h染色体畸变为阴性。结论高纯度大豆卵磷脂不能引起CHL细胞染色体产生畸变作用。 相似文献
136.
A new type of prosome-like particle, composed of small cytoplasmic RNA and multimers of a 21-kDa protein, inhibits protein synthesis in vitro 总被引:3,自引:0,他引:3
O Akhayat A A Infante D Infante C Martins de SA M F Grossi de SA K Scherrer 《European journal of biochemistry》1987,170(1-2):23-33
A large fraction of the translationally repressed non-globin messenger RNA in duck erythroblasts is present in non-polyribosomal free mRNP structures which sediment in the 30-40-S range ('35 S'). In 0.5 M KCl, they form core complexes which show a pronounced peak at about 32 S containing mRNA and a discrete spherical RNP particle with a diameter of about 12 nm and the typical morphology of a prosome [H.-P. Schmid et al. (1984) EMBO J. 3, 29-34]. Buoyant density measurements and chromatography on oligo(dT)-cellulose indicate that this particle is bound to mRNA; it can be released from the mRNA by treatment of the free mRNP fraction with SDS. This prosome-like particle inhibits the translation of mRNA in vitro. It is composed primarily of multimers of a single 21-kDa protein and at least one species of RNA of about 80-100 nucleotides. It is resistant to dissociation by 2 M CS2SO4 and 1% SDS; the 21-kDa protein is not attacked by proteinase K unless the particle is extracted with phenol prior to treatment with the protease. The small RNA moiety of the particle hybridizes to the poly(A)-rich mRNA derived from the free mRNPs, as well as to polyribosomal mRNA. These data indicate that prosomes may serve to regulate mRNA translation; they show furthermore that prosome-like particles (about 600 kDa mass) may be built of up to 25 molecules of a single specific protein, rather than of the entire set of about 20 prosomal proteins previously identified. 相似文献
137.
Basolateral K channels in an insect epithelium. Channel density, conductance, and block by barium 下载免费PDF全文
K channels in the basolateral membrane of insect hindgut were studied using current fluctuation analysis and microelectrodes. Locust recta were mounted in Ussing-type chambers containing Cl-free saline and cyclic AMP (cAMP). A transepithelial K current was induced by raising serosal [K] under short-circuit conditions. Adding Ba to the mucosal (luminal) side under these conditions had no effect; however, serosal Ba reversibly inhibited the short-circuit current (Isc), increased transepithelial resistance (Rt), and added a Lorentzian component to power density spectra of the Isc. A nonlinear relationship between corner frequency and serosal [Ba] was observed, which suggests that the rate constant for Ba association with basolateral channels increased as [Ba] was elevated. Microelectrode experiments revealed that the basolateral membrane hyperpolarized when Ba was added: this change in membrane potential could explain the nonlinearity of the 2 pi fc vs. [Ba] relationship if external Ba sensed about three-quarters of the basolateral membrane field. Conventional microelectrodes were used to determine the correspondence between transepithelially measured current noise and basolateral membrane conductance fluctuations, and ion-sensitive microelectrodes were used to measure intracellular K activity (acK). From the relationship between the net electrochemical potential for K across the basolateral membrane and the single channel current calculated from noise analysis, we estimate that the conductance of basolateral K channels is approximately 60 pS, and that there are approximately 180 million channels per square centimeter of tissue area. 相似文献
138.
Phosphate Regulation of Nitrate Assimilation in Soybean 总被引:24,自引:1,他引:23
RUFTY THOMAS W. JR; ISRAEL DANIEL W.; VOLK RICHARD J.; QIU JINSHU; SA TONGMIN 《Journal of experimental botany》1993,44(5):879-891
It is known that phosphorus deficiency results in alterationsin the assimilation of nitrogen. An experiment was conductedto investigate mechanisms involved in altered 15NO3 uptake,endogenous 15N translocation, and amino acid accumulation insoybean (Glycine max L. Merrill, cv. Ransom) plants deprivedof an external phosphorus supply for 20 d in solution culture.Phosphorus deprivation led to decreased rates of 15NO3uptake and increased accumulation of absorbed 15N in the root.Both effects became more pronounced with time. Asparagine, theprimary transport amino acid in soybean, accumulated in largeexcess in roots and stems. In roots of phosphorus-deprived plants,concentrations of ATP and inorganic phosphate declined rapidly,but dry weight accumulation was similar to or above that ofthe control even after 20 d of treatment. Arginine accumulationin leaves was greatly enhanced, even though 15N partitioninginto the insoluble reduced-N fraction of leaves was unaffected.The results suggest that decreases in NO3 uptake in lowphosphorus plants could be caused by feedback control factorsand by limited ATP availability. The decline in endogenous Ntransport from the root to the shoot may be associated withchanges in membrane properties, which also result in paralleleffects on hydraulic conductance and the upward flow of waterthrough the plant. Key words: Phosphorus stress, nitrate uptake, nitrate translocation, arginine 相似文献
139.
140.
In etiolated pea and maize leaves illuminated after incubation at 38 degreesC, a new dark reaction was shown manifested in the bathochromic shift of spectral bands and accompanied by esterification of the product of protochlorophyllide photochemical reduction--Chld 684/676: Chld 684/676 --> Chl 688/680. After completion of the reaction a rapid (20-30 sec) quenching of the fluorescence of the reaction product (Chl 688/680) was observed. The reaction Chld 684/676 --> Chl 688/680 is inhibited under anaerobic conditions and in the presence of cyanide; the reaction accompanied by Chl 688/680 fluorescence quenching is not observed in pea mutants with impaired function of photosystem II reaction centers. The spectral properties of the formed Chl form with the absorption maximum at 680 nm, fluorescence quenching, and simultaneous synthesis of pheophytin suggest that the reaction is connected with the chlorophyll of photosystem II reaction center--P-680. 相似文献