全文获取类型
收费全文 | 8629篇 |
免费 | 790篇 |
出版年
2023年 | 89篇 |
2022年 | 182篇 |
2021年 | 324篇 |
2020年 | 190篇 |
2019年 | 237篇 |
2018年 | 277篇 |
2017年 | 236篇 |
2016年 | 371篇 |
2015年 | 574篇 |
2014年 | 554篇 |
2013年 | 671篇 |
2012年 | 783篇 |
2011年 | 733篇 |
2010年 | 473篇 |
2009年 | 361篇 |
2008年 | 505篇 |
2007年 | 441篇 |
2006年 | 394篇 |
2005年 | 338篇 |
2004年 | 315篇 |
2003年 | 281篇 |
2002年 | 247篇 |
2001年 | 48篇 |
2000年 | 33篇 |
1999年 | 52篇 |
1998年 | 63篇 |
1997年 | 39篇 |
1996年 | 34篇 |
1995年 | 32篇 |
1994年 | 30篇 |
1993年 | 29篇 |
1992年 | 16篇 |
1991年 | 26篇 |
1990年 | 27篇 |
1989年 | 22篇 |
1988年 | 18篇 |
1987年 | 21篇 |
1986年 | 23篇 |
1985年 | 21篇 |
1984年 | 30篇 |
1983年 | 25篇 |
1982年 | 28篇 |
1981年 | 21篇 |
1980年 | 14篇 |
1979年 | 19篇 |
1978年 | 14篇 |
1977年 | 12篇 |
1976年 | 14篇 |
1975年 | 10篇 |
1972年 | 10篇 |
排序方式: 共有9419条查询结果,搜索用时 31 毫秒
31.
Mordechai Schreiber Leon Fogelfeld Miry C. Souroujon Fortune Kohen Sara Fuchs 《Life sciences》1983,33(15):1519-1526
Spiroperidol was covalently conjugated to bovine serum albumin (BSA). Conjugated spiroperidol was almost as efficient as free spiroperidol in its binding capacity to dopamine receptor. Antibodies to spiroperidol were produced in rabbits following repeated immunizations with the conjugate of spiroperidol and BSA. The obtained antibodies have an apparent KD of 0.02 nM for [3H]-spiroperidol. These antibodies bind also to other butyrophenones with IC50 values three to four orders of magnitude higher than the IC50 obtained with unlabeled spiroperidol. Antibodies were purified from anti-spiroperidol sera by affinity chromatography. Anti-idiotypic antibodies were raised in rabbits by immunization with the purified anti-spiroperidol antibodies. Some rabbits produced anti-idiotypic antibodies which bind to rat and calf striatum. 相似文献
32.
Cytochemical and immunocytochemical methods were used to localize photosystems I and II in barley (Hordeum vulgare L. cv Himalaya) chloroplasts. PSI activity, monitored by diaminobenzidine oxidation, was associated with the lumen side of the thylakoids of both grana and stroma lamellae. The P700 chlorophyll a protein, the reaction center of PSI, was localized on thin sections of barley chloroplasts using monospecific antibodies to this protein and the peroxidase-antiperoxidase procedure. Results obtained by immunocytochemistry were similar to those of the diaminobenzidine oxidation: both grana and stroma lamellae contained immunocytochemically reactive material. Both the grana and stroma lamellae were also labeled when isolated thylakoids were reacted with the P700 chlorophyll a protein antiserum and then processed by the peroxidase-antiperoxidase procedure. PSII activity was localized cytochemically by monitoring the photoreduction of thiocarbamyl nitroblue tetrazolium, a reaction sensitive to the PSII inhibitor, DCMU. PSII reactions occurred primarily on the grana lamellae, with weaker reactions on the stroma lamellae. 相似文献
33.
Specific Determination of alpha-Amylase Activity in Crude Plant Extracts Containing beta-Amylase
下载免费PDF全文
![点击此处可从《Plant physiology》网站下载免费的PDF全文](/ch/ext_images/free.gif)
The specific measurement of α-amylase activity in crude plant extracts is difficult because of the presence of β-amylases which directly interfere with most assay methods. Methods compared in this study include heat treatment at 70°C for 20 min, HgCl2 treatment, and the use of the α-amylase specific substrate starch azure. In comparing alfalfa (Medicago sativa L.), soybeans (Glycine max [L.] Merr.), and malted barley (Hordeum vulgare L.), the starch azure assay was the only satisfactory method for all tissues. While β-amylase can liberate no color alone, over 10 International units per milliliter β-amylase activity has a stimulatory effect on the rate of color release. This stimulation becomes constant (about 4-fold) at β-amylase activities over 1,000 International units per milliliter. Two starch azure procedures were developed to eliminate β-amylase interference: (a) the dilution procedure, the serial dilution of samples until β-amylase levels are below levels that interfere; (b) the β-amylase saturation procedure, addition of exogenous β-amylase to increase endogenous β-amylase activity to saturating levels. Both procedures yield linear calibrations up to 0.3 International units per milliliter. These two procedures produced statistically identical results with most tissues, but not for all tissues. Differences between the two methods with some plant tissues was attributed to inaccuracy with the dilution procedure in tissues high in β-amylase activity or inhibitory effects of the commercial β-amylase. The β-amylase saturation procedure was found to be preferable with most species. The heat treatment was satisfactory only for malted barley, as α-amylases in alfalfa and soybeans are heat labile. Whereas HgCl2 proved to be a potent inhibitor of β-amylase activity at concentrations of 10 to 100 micromolar, these concentrations also partially inhibited α-amylase in barley malt. The reported α-amylase activities in crude enzyme extracts from a number of plant species are apparently the first specific measurements reported for any plant tissues other than germinating cereals. 相似文献
34.
Gabriella Goldberg Daria Mochly-Rosen Sara Fuchs Yoram Lass 《The Journal of membrane biology》1983,76(2):123-128
Summary Monoclonal antibodies directed against the cholinergic binding site of the acetylcholine receptor were found to alter the ion channel properties in cultured chick myoballs. Time and dose dependent reduction in acetylcholine sensitivity was observed. Noise analysis experiments indicated a decrease in the mean single channel conductance and an increase in the mean single channel open time. 相似文献
35.
The effect of osmotic `shock'' on the swelling pattern and respiratory control of rat-liver mitochondria 总被引:2,自引:2,他引:0
1. Rat-liver mitochondria suspended in 0.25m-sucrose were exposed for a few seconds to strongly hypo-osmotic conditions, and then the osmolarity of the medium was raised again to 0.25 with the aid of tris chloride (osmotic ;shock'). 2. Mitochondria after hypo-osmotic pretreatment lost their capacity for slow energy-dependent swelling in iso-osmotic tris buffer and showed no respiratory control. 3. Swelling could be induced in the ;shocked' mitochondria by ATP but not by addition of respiratory substrates. 4. It was shown that cytochrome c is lost from ;shocked' mitochondria when they come into contact with the tris buffer present in the assay medium, and that the changes observed in the pattern of swelling, as well as in respiratory control, are directly connected with this loss of cytochrome c. 5. The results of the investigation are discussed with regard to the role of cytochrome c in swelling and respiratory control. 相似文献
36.
The 5-fluorouracil (5 FU) technique for the phenotypic reversion of amber mutants was used to demonstrate that under certain circumstances, in the presence of putrescine or spermidine, early mutants have an enhanced response to 5 FU, whereas late mutants have a delayed response. Bacteria infected by T4D wild-type bacteriophage did not produce phage in the presence of high putrescine concentrations. Pulse treatments with putrescine showed that the production of lysozyme depends on a putrescine-sensitive process that begins immediately after infection at 26 C and ends at 36 min or even later. The addition of putrescine at any time during the critical period between 0 and 36 min led to a corresponding delay in lysozyme synthesis after the inhibitor was removed. Intracellular phage maturation was delayed by the addition of 100 mumoles of putrescine per ml. Early enzymes were not affected by the diamine, but the level of phage deoxyribonucleic acid was considerably decreased by the inhibitor. The putrescine-sensitive process that affects the timing of maturation is suggested to be the natural process controlling the T4 "clock." 相似文献
37.
Conformational change accompanying modification of myosin ATPase 总被引:4,自引:0,他引:4
38.
1. Three random linear copolymers composed of two or three of the amino acids d-tyrosine, d-glutamic acid, d-alanine and d-lysine, and a branched multichain copolymer with a poly-d-lysine backbone and polymeric side chains of d-tyrosine and d-glutamic acid, were found to be non-antigenic in rabbits, by precipitin and passive cutaneous anaphylaxis, and in guinea pigs, by delayed hypersensitivity tests. The corresponding four copolymers of l-amino acids were shown to be antigenic by all the three criteria. 2. No immunological cross-reactions were observed between the polypeptides composed of d-amino acids and the corresponding l-amino acid copolymers. 3. Similarly, an azobenzenearsonic acid conjugate of poly-d-tyrosine was shown to be non-antigenic in guinea pigs, in contrast with an analogous conjugate of poly-l-tyrosine. Animals sensitized with the conjugate of poly-l-tyrosine did not exhibit delayed skin reactions, when cross-tested with the d-conjugate. 4. A linear polymer composed of d-tyrosine, l-glutamic acid and l-alanine was found to be immunogenic and to cross-react with the corresponding polymer composed exclusively of d-amino acids. 相似文献
39.
Summary The giant salamanders of North America include 4 genera, all of which are aquatic. We have compared the efficacy of aquatic
O2 uptake among them by measuring theVO2 while submerged and determining the responses to progressive hypoxia at 10–240 mmHg at 20° C. Both species ofAmphiuma were metabolic O2 conformers over the entire range ofPO2. About half ofSiren lacertina were conformers over this range, and half were regulators with an average critical O2 tension of 92 mmHg. There were no short-term changes (days) in the response ofSiren to progressive hypoxia, but one animal switched from conformation to regulation after 4–5 months. Neither genus is considered
to have an exceptionally low metabolic rate. The “whole-body O2 conductance”, defined asΔVO2/ΔPO2(μl O2 · g−1 · h−1 · mmHg−1) in the range of metabolic O2 conformity, was least in the species most dependent upon air-breathing and most likely to be found in hypoxic waters (e.g.,
0.076 forAmphiuma), and greatest in those that airbreathe less frequently and/or are found in relatively normoxic waters (e.g., 0.429 forNecturus). These conductances are considered to be adaptive in terms of preventing O2 loss through the skin, or in facilitating its uptake, as correlated with the O2 tensions normally prevailing in the environment of each species. 相似文献