全文获取类型
收费全文 | 4826篇 |
免费 | 268篇 |
国内免费 | 517篇 |
出版年
2023年 | 56篇 |
2022年 | 66篇 |
2021年 | 101篇 |
2020年 | 99篇 |
2019年 | 151篇 |
2018年 | 168篇 |
2017年 | 112篇 |
2016年 | 130篇 |
2015年 | 114篇 |
2014年 | 263篇 |
2013年 | 282篇 |
2012年 | 199篇 |
2011年 | 277篇 |
2010年 | 212篇 |
2009年 | 208篇 |
2008年 | 240篇 |
2007年 | 225篇 |
2006年 | 211篇 |
2005年 | 209篇 |
2004年 | 156篇 |
2003年 | 158篇 |
2002年 | 129篇 |
2001年 | 118篇 |
2000年 | 92篇 |
1999年 | 76篇 |
1998年 | 77篇 |
1997年 | 70篇 |
1996年 | 74篇 |
1995年 | 61篇 |
1994年 | 65篇 |
1993年 | 76篇 |
1992年 | 72篇 |
1991年 | 66篇 |
1990年 | 71篇 |
1989年 | 59篇 |
1988年 | 53篇 |
1987年 | 57篇 |
1986年 | 32篇 |
1985年 | 58篇 |
1984年 | 102篇 |
1983年 | 75篇 |
1982年 | 90篇 |
1981年 | 76篇 |
1980年 | 64篇 |
1979年 | 65篇 |
1978年 | 35篇 |
1977年 | 45篇 |
1976年 | 32篇 |
1975年 | 28篇 |
1974年 | 25篇 |
排序方式: 共有5611条查询结果,搜索用时 31 毫秒
11.
Monoclonal antibodies against chick embryonic beta-galactoside-binding lectin were obtained. One of the monoclonal antibodies was ineffective in Western blotting and seemed to be unable to bind the SDS-denatured lectin. When the native lectin was dotted on a nitrocellulose filter and subjected to denaturation by treatment with SDS, urea or heat, binding of this antibody no longer occurred, though other monoclonal antibodies bound normally. This antibody seems to have been raised against an epitope which is destroyed upon denaturation. 相似文献
12.
Inorganic phosphate determination in the presence of a labile organic phosphate: assay for carbamyl phosphate phosphatase activity 总被引:3,自引:0,他引:3
A periodate-resorcinol method for bound sialic acid using the Technicon Autoanalyzer II is presented. It has a sensitivity similar to the manual method, is linear between 5 and 65 nmol/ml, requires less than 0.2 ml of sample, and can be run at the rate of 70 samples/h. Little cross-reaction with common matrix and cell components was found. The method is compatible with many commonly used volatile and nonvolatile chromatographic buffers. The use of a bound sialic acid standard such as N-acetylneuraminyl lactose is recommended. 相似文献
13.
Glycophorin, an integral membrane glycoprotein known to be a receptor for several lectins, has been spin labelled specifically on headgroup terminal sugars. The labelled derivative has been studied in solution and also in various model membranes in an attempt to determine the factors which control headgroup dynamics. Under conditions which mimic those in a living cell the oligosaccharide chains show a uniform, relatively high freedom of motion, with individual sugar correlation times on the order of 6 × 10?10 sec to 8 × 10?10 sec depending upon the extent of glycoprotein headgroup involvement with other glycocalyx components. They exhibit no detectable occupancy of lipid or protein hydrophobic domains. Oligosaccharide dynamics are insensitive to factors which act upon that portion of the polypeptide backbone which inserts into the membrane, however a specific recognition event markedly reduces terminal sugar mobility. 相似文献
14.
There was little release of extractable SO4-S during four weeks from CS2 applied by injecting into two S-deficient soils. In this incubation experiment, the rate of CS2 was 30 μg S g−, placement was injection at 9 cm depth, soil temperature was 20°C, and soil moisture tension was 33 kPa. The yield of barley
forage after seven weeks in the greenhouse showed only small increases from 10 or 30 μg S g−1 of CS2 as compared to Na2SO4, on the two soils.
While CS2 supplied little plant available S in the short term, it was an effective inhibitor of nitrification. In the laboratory, or
in the field, the injection of CS2 (with N fertilizers) at a point 9 cm into the soils either stopped or reduced nitrification. In one laboratory experiment,
35 μg of CS2 g−1 of soil with urea reduced nitrification for at least four weeks; and in another experiment 20 μg of CS2 g−1 of soil with aqua NH3 nearly or completely inhibited nitrification at 20 days. In two field experiments, 3 and 12 μg of CS2 g−1 of soil (or 6 and 24 kg ha−1) with aqua NH3 inhibited nitrification from October to the subsequent May. In addition, CS2 reduced the amount of ammonium produced from the soil N, both in these two field experiments and in the laboratory experiments.
That is to say, CS2 injected at a point, inhibited both nitrification and ammonification.
In other field experiments, CS2 at a rate of 10 kg ha−1 was injected in bands 9 cm deep with urea in October, and by May there was still reduced nitrification. Less than half of
the fall-applied urea alone was recovered as mineral N, but with the application of CS2 the recovery was increased to three-quarters.
The yield and N uptake of barley grain was increased where fall-applied banded urea or aqua NH3 received banded CS2, (NH4)2CS3, or K2CS3. The average increase in yield from fall-applied fertilizer, from inhibitor with fall-applied fertilizer, and from spring-applied
fertilizer was 800, 1370, and 1900 kg ha−1, respectively. In the same order, the apparent % recovery of fertilizer N in grain was 24, 42, and 60. 相似文献
15.
16.
Minjuan Shen Mingli Lin Mengqi Zhu Wenxin Zhang Danyang Lu Huanhuan Liu Jingjing Deng Kehua Que Xu Zhang 《Biochimica et Biophysica Acta (BBA)/General Subjects》2019,1863(1):167-181
Since their discovery, matrix vesicles (MVs) containing minerals have received considerable attention for their role in the mineralization of bone, dentin and calcified cartilage. Additionally, MVs' association with collagen fibrils, which serve as the scaffold for calcification in the organic matrix, has been repeatedly highlighted. The primary purpose of the present study was to establish a MVs–mimicking model (PEG-S-ACP/micelle) in vitro for studying the exact mechanism of MVs-mediated extra/intra fibrillar mineralization of collagen in vivo. In this study, high-concentration serine was used to stabilize the amorphous calcium phosphate (S-ACP), which was subsequently mixed with polyethylene glycol (PEG) to form PEG-S-ACP nanoparticles. The nanoparticles were loaded in the polysorbate 80 micelle through a micelle self-assembly process in an aqueous environment. This MVs–mimicking model is referred to as the PEG-S-ACP/micelle model. By adjusting the pH and surface tension of the PEG-S-ACP/micelle, two forms of minerals (crystalline mineral nodules and ACP nanoparticles) were released to achieve the extrafibrillar and intrafibrillar mineralization, respectively. This in vitro mineralization process reproduced the mineral nodules mediating in vivo extrafibrillar mineralization and provided key insights into a possible mechanism of biomineralization by which in vivo intrafibrillar mineralization could be induced by ACP nanoparticles released from MVs. Also, the PEG-S-ACP/micelle model provides a promising methodology to prepare mineralized collagen scaffolds for repairing bone defects in bone tissue engineering. 相似文献
17.
Ronald J.A. Wanders Carlo Van Roermund Cor Lof Alfred J. Meijer 《Analytical biochemistry》1983,129(1):80-87
A simple fluorimetric assay for the determination of carbamoyl phosphate in tissue extracts is described. In the assay, production of ATP from carbamoyl phosphate and ADP by carbamate kinase is coupled to the formation of NADPH, using glucose, hexokinase, NADP+, and glucose-6-phosphate dehydrogenase. Production of NADPH in this system proved to be equal to the amount of carbamoyl phosphate present. 相似文献
18.
Janet E. Clements Barbara B. Anderson 《Biochimica et Biophysica Acta (BBA)/General Subjects》1980,632(2):159-163
The red-cell enzymes, glutathione reductase (FAD-dependent) and pyridoxine (pyridoxamine) phosphate oxidase (FMN-dependent), were studied in control subjects. The wide range the glutathione reductase activity correlated inversely with the percentage stimulation by FAD added in vitro, and with pyridoxine (pyridoxamine) phosphate oxidase activity. Both enzymes were stimulated after ingestion of riboflavin. The results support the suggestion that the rate of metabolism of riboflavin in the red cell controls the activity of both enzymes, and the rate of red-cell metabolism of vitamin B-6. 相似文献
19.
Aaron J. Oakley 《Biochemical and biophysical research communications》2010,397(4):745-224
Phytases hydrolyse the phosphomonoesters of phytate (myo-inositol-1,2,3,4,5,6-hexakis phosphate) and thus find uses in plant and animal production through the mobilisation of phosphorus from this source. The structure of partially deglycosylated Aspergillus niger PhyA is presented in apo form and in complex with the potent inhibitor myo-inositol-1,2,3,4,5,6-hexakis sulfate, which by analogy with phytate provides a snapshot of the Michaelis complex. The structure explains the enzyme’s preference for the 3′-phosphate of phytate. The apo-and inhibitor-bound forms are similar and no induced-fit mechanism operates. Furthermore the enzyme structure is apparently unaffected by the presence of glycosides on the surface. The new structures of A. niger PhyA are discussed in the context of protein engineering studies aimed at modulating pH preference and stability. 相似文献
20.
R. Brändén T. Nilsson S. Styring 《Biochemical and biophysical research communications》1980,92(4):1297-1305
A sensitive and reliable method to determine the stereochemical composition of 3-phosphoglyceric acid is presented. Results obtained with this method show that 3-phosphoglyceric acid formed in the ribulose-1,5-bisphosphate carboxylase reaction is a mixture of 10% L-3-PGA and 90% D-3-PGA. 相似文献