全文获取类型
收费全文 | 3227篇 |
免费 | 238篇 |
国内免费 | 2篇 |
出版年
2023年 | 24篇 |
2022年 | 48篇 |
2021年 | 96篇 |
2020年 | 58篇 |
2019年 | 60篇 |
2018年 | 97篇 |
2017年 | 67篇 |
2016年 | 120篇 |
2015年 | 165篇 |
2014年 | 165篇 |
2013年 | 227篇 |
2012年 | 284篇 |
2011年 | 261篇 |
2010年 | 176篇 |
2009年 | 143篇 |
2008年 | 232篇 |
2007年 | 191篇 |
2006年 | 198篇 |
2005年 | 139篇 |
2004年 | 133篇 |
2003年 | 130篇 |
2002年 | 118篇 |
2001年 | 25篇 |
2000年 | 16篇 |
1999年 | 24篇 |
1998年 | 18篇 |
1997年 | 19篇 |
1996年 | 16篇 |
1995年 | 21篇 |
1994年 | 17篇 |
1993年 | 15篇 |
1992年 | 15篇 |
1991年 | 10篇 |
1990年 | 7篇 |
1989年 | 14篇 |
1987年 | 8篇 |
1986年 | 4篇 |
1985年 | 9篇 |
1983年 | 9篇 |
1982年 | 17篇 |
1981年 | 8篇 |
1980年 | 6篇 |
1979年 | 4篇 |
1977年 | 5篇 |
1976年 | 4篇 |
1975年 | 4篇 |
1974年 | 4篇 |
1972年 | 7篇 |
1971年 | 4篇 |
1970年 | 5篇 |
排序方式: 共有3467条查询结果,搜索用时 312 毫秒
1.
Peng Chen Pranjal Swarup Wojciech Michal Matkowski Adams Wai Kin Kong Su Han Zhihe Zhang Hou Rong 《Ecology and evolution》2020,10(7):3561-3573
- As a highly endangered species, the giant panda (panda) has attracted significant attention in the past decades. Considerable efforts have been put on panda conservation and reproduction, offering the promising outcome of maintaining the population size of pandas. To evaluate the effectiveness of conservation and management strategies, recognizing individual pandas is critical. However, it remains a challenging task because the existing methods, such as traditional tracking method, discrimination method based on footprint identification, and molecular biology method, are invasive, inaccurate, expensive, or challenging to perform. The advances of imaging technologies have led to the wide applications of digital images and videos in panda conservation and management, which makes it possible for individual panda recognition in a noninvasive manner by using image‐based panda face recognition method.
- In recent years, deep learning has achieved great success in the field of computer vision and pattern recognition. For panda face recognition, a fully automatic deep learning algorithm which consists of a sequence of deep neural networks (DNNs) used for panda face detection, segmentation, alignment, and identity prediction is developed in this study. To develop and evaluate the algorithm, the largest panda image dataset containing 6,441 images from 218 different pandas, which is 39.78% of captive pandas in the world, is established.
- The algorithm achieved 96.27% accuracy in panda recognition and 100% accuracy in detection.
- This study shows that panda faces can be used for panda recognition. It enables the use of the cameras installed in their habitat for monitoring their population and behavior. This noninvasive approach is much more cost‐effective than the approaches used in the previous panda surveys.
2.
3.
4.
Drahomíra Kenov Lucie oltysov Michal Pravenec Marie-Pierre Moisan W. Theodore Kurtz Vladimír Ken 《Journal of Experimental Animal Science》2000,41(1-2)
The SHR-Lx congenic strain carrying a differential segment of chromosome 8 of BN and PD origin was recently shown to exhibit a significant decrease in blood pressure as compared to the SHR strain. There were two positional candidate genes for blood pressure control mapped to the differential segment: the rat kidney epithelial potassium channel gene (Kcnj1) and brain dopamine receptor 2 gene (Drd2). Bot these genes were separated into SHR.BN-RNO8 congenic substrains. In this communication, we are presenting the assignment of two further putative candidate genes, which might be involved in blood pressure control to the BN/PD differential segment of the SHR-Lx congenic strain. These are: the gene coding for smooth muscle cell specific protein 22 (Sm22) defined by the D8Mcw1 marker and neuronal nicotinic acetylcholine receptor gene cluster, defined by the D8Bord1 marker. Moreover, the glutamate receptor gene Grik4 which also maps to the differential segment of the SHR-Lx should be taken into account. The genetic separation of all these putative candidate genes of blood pressure control is being performed by recombinations and subsequent selection using (SHR×SHR-Lx) intercross population. 相似文献
5.
6.
7.
N. Gilboa-Garber V. Zakut L. Mizrahi 《Biochimica et Biophysica Acta (BBA)/General Subjects》1973,297(1):120-124
Production of cholinesterase by a pyocyanin-producing strain of Pseudomonas aeruginosa, isolated from a patient and grown in the presence of acetylcholine as the main source of carbon, was described. The enzyme activity was detected in suspensions of intact bacteria and in their subcellular preparations. Like the acetylcholinesterase of the electric eel, as opposed to that of the erythrocytes, this bacterial enzyme was inhibited by specific antiserum produced against it in rabbits. The production of the enzyme was found to be sensitive to catabolite repression and to require external cyclic AMP, but not 5′-AMP for the elimination of this repression. Cyclic AMP alone, without the inducer, did not stimulate the production of the enzyme. 相似文献
8.
Michal Gadot Ouriel Faktor Shalom W. Applebaum 《Archives of insect biochemistry and physiology》1987,4(1):17-27
Reserpine, at doses of 20–175 μg per g body weight, severely retards oogenesis in newly emerged adult female migratory locusts (Locusta migratoria migratorioides) but does not increase mortality during the first 9 days and only slightly delays somatic growth. Total protein, and hemolymph vitellogenin content particularly, are significantly reduced in reserpine-treated locusts. The synthesis of juvenile hormone III (JH-III) following adult emergence, essential for induction of vitellogenesis and subsequent oogenesis, is dependent on the maturation and activation of the corpora allata (CA). CA of 7- to 8-day-old female locusts, treated with reserpine at day 1 after adult emergence, are only marginally active in vitro and are only slightly stimulated by an allatotropic factor. The basal activity and response of CA from the reserpine-treated locusts resembles that of newly emerged locusts, suggesting that reserpine specifically retards the initial maturation of the locust CA. Recovery of basal CA activity is evident on days 12–13 in reserpine-treated locusts, but responsiveness to the allatotropic factor is not recovered. Starvation of newly emerged females for 3 days and subsequent feeding did not effect ooctye development or CA activity. Cerebral content of the allatotropic factor, assayed on days 7–8, is not reduced by the reserpine treatment. 相似文献
9.
Michal Gadot Ada Rafaeli Shalom W. Applebaum 《Archives of insect biochemistry and physiology》1987,4(3):213-223
Methanol extracts of locust brains, corpora cardiaca (CC), and suboesophageal ganglia (SOG) were separated by gradient and/or isocratic reverse-phase high-performance liquid chromatography (HPLC) and allatotropic activity monitored in the eluted fractions. A major peak of activity, separated by isocratic separation with 12% 2-propanol, designated allatotropin I, exhibited identical retention times in the three tissue extracts. Doseresponse curves of allatotropin I indicate similar content in brain and CC-equivalents, whereas optic lobes, similarly separated by isocratic HPLC, contain only one-tenth of this amount of allatotropin. Allatotropin I is resistant to boiling and is susceptible to tryptic and chymotryptic digestion. Methanol extracts of thoracic muscle, Malpighian tubules, fat body or ovaries, similarly prepared and boiled, did not exhibit allatotropic activity at high doses of tissue equivalents. 相似文献
10.
Kinetic mechanism of DNA polymerase I (Klenow) 总被引:12,自引:0,他引:12
The minimal kinetic scheme for DNA polymerization catalyzed by the Klenow fragment of DNA polymerase I (KF) from Escherichia coli has been determined with short DNA oligomers of defined sequence. A key feature of this scheme is a minimal two-step sequence that interconverts the ternary KF.DNAn.dNTP and KF.DNAn+1.PPi complexes. The rate is not limited by the actual polymerization but by a separate step, possibly important in ensuring fidelity [Mizrahi, V., Henrie, R. N., Marlier, J. F., Johnson, K. A., & Benkovic, S. J. (1985) Biochemistry 24, 4010-4018]. Evidence for this sequence is supplied by the observation of biphasic kinetics in single-turnover pyrophosphorolysis experiments (the microscopic reverse of polymerization). Data analysis then provides an estimate of the internal equilibrium constant. The dissociations of DNA, dNTP, and PPi from the various binary and ternary complexes were measured by partitioning (isotope-trapping) experiments. The rate constant for DNA dissociation from KF is sequence dependent and is rate limiting during nonprocessive DNA synthesis. The combination of single-turnover (both directions) and isotope-trapping experiments provides sufficient information to permit a quantitative evaluation of the kinetic scheme for specific DNA sequences. 相似文献