全文获取类型
收费全文 | 4353篇 |
免费 | 216篇 |
国内免费 | 27篇 |
出版年
2024年 | 11篇 |
2023年 | 80篇 |
2022年 | 187篇 |
2021年 | 350篇 |
2020年 | 167篇 |
2019年 | 193篇 |
2018年 | 283篇 |
2017年 | 173篇 |
2016年 | 244篇 |
2015年 | 305篇 |
2014年 | 333篇 |
2013年 | 326篇 |
2012年 | 341篇 |
2011年 | 304篇 |
2010年 | 184篇 |
2009年 | 174篇 |
2008年 | 176篇 |
2007年 | 146篇 |
2006年 | 112篇 |
2005年 | 108篇 |
2004年 | 82篇 |
2003年 | 62篇 |
2002年 | 46篇 |
2001年 | 11篇 |
2000年 | 16篇 |
1999年 | 12篇 |
1998年 | 17篇 |
1997年 | 12篇 |
1996年 | 12篇 |
1995年 | 12篇 |
1994年 | 8篇 |
1993年 | 8篇 |
1992年 | 11篇 |
1991年 | 5篇 |
1990年 | 4篇 |
1989年 | 6篇 |
1988年 | 7篇 |
1987年 | 7篇 |
1986年 | 3篇 |
1985年 | 5篇 |
1984年 | 4篇 |
1982年 | 5篇 |
1981年 | 5篇 |
1980年 | 9篇 |
1979年 | 3篇 |
1978年 | 4篇 |
1976年 | 4篇 |
1975年 | 2篇 |
1974年 | 8篇 |
1971年 | 3篇 |
排序方式: 共有4596条查询结果,搜索用时 15 毫秒
941.
Kazuaki Tanaka Takahiro Yamagata Joseph S. Masangkay Muhammad O. Faruque Dang Vu-Binh Salundik Sri Supraptini Mansjoer Yoshi Kawamoto Takao Namikawa 《Biochemical genetics》1995,33(5-6):137-148
Cleavage patterns of mitochondrial DNAs (mtDNAs) by 15 restriction endonucleases were analyzed for 10 swamp and 13 river types of domestic water buffaloes. Digestions with nine enzymes exhibited polymorphisms giving two or three kinds of cleavage patterns. Five mtDNA types were identified, three types in the swamp buffaloes of the Philippines, Vietnam, and Indonesia (S-types) and two types in the river buffaloes of Bangladesh and Pakistan (R-types). Nucleotide diversities ranged from 0.2 to 0.6% within the S- and R-types and from 1.9 to 2.4% between the R-types and the S-types. These values indicated that R-type and S-type mtDNAs differentiated at thesubspecific level of other mammalianspecies reported. The possibility of polyphyletic domestication in different places is discussed for the origin of two distinct types of domestic water buffaloes. 相似文献
942.
Summary A strategy for the production of non-inhibitory polyclonal antisera for the immobilization of glycoenzymes is described. Insoluble complexes of invertase prepared using antiinvertase glycosyl antisera were more resistant to heat and urea induced denaturation than those prepared using antiinvertase antisera from which the glycosyl specific antibodies were removed. Unfractionated antiinvertase antibodies however gave most stable immunocomplexes with invertase. 相似文献
943.
S. Marvin Friedman Muhammad Malik Karl Drlica 《Molecular genetics and genomics : MGG》1995,248(4):417-422
A spontaneously occurring, nalidixic acid-resistant (NalR), thermotolerant (T/r) mutant ofEscherichia coli was isolated. Bacteriophage P1-mediated transduction showed that NalR mapped at or neargyr A, one of the two genes encoding DNA gyrase. Expression ofgyrA + from a plasmid rendered the mutant sensitive to nalidixic acid and to high temperature, the result expected for alleles mapping ingyrA. Plasmid linking number measurements, made with DNA from cells grown at 37° C or shifted to 48° C, revealed that supercoiling was about 12% less negative in the T/r mutant than in the parental strain. Each strain preferentially expressed two different proteins at 48° C. The genetic and supercoiling data indicate that thermo-tolerance can arise from an alteration in DNA gyrase that lowers supercoiling. This eubacterial study, when. coupled with those of archaebacteria, suggests that DNA relaxation is a general aspect of thermotolerance. 相似文献
944.
Khawar Sohail Siddiqui Abdul Aala Najmus Saqib Mohammad Hamid Rashid Mohammad Ibrahim Rajoka 《Biotechnology letters》1997,19(4):325-330
The carboxyl groups of purified carboxymethylcellulase (CMCase) from Aspergillus niger NIAB280 were modified by 1-ethyl-3(3-dimethylaminopropyl) carbodiimide (EDC) in the presence of glycinamide for 15 min (GAM15) and glycinamide plus cellobiose for 75 min (GAM75). The half-lives of GAM15 at different temperatures were significantly enhanced whereas those of GAM75 were reduced as compared with the native CMCase. The activation energies of denaturation of native, GAM15 and GAM75 were 40, 35 and 59kJ mol respectively. Native CMCase and GAM15 showed no compensation effect, whereas native and GAM75 gave temperature of compensation of 44¡C. Gibb's free energy of activation for denaturation (DG*) of GAM15 was increased as compared with native CMCase. Surprisingly the entropies (DS*) of activation for denaturation were negative for native and GAM75 and decreased further for GAM15 between the temperature range of 45 to 65¡C. A possible explanation for the thermal inactivation of native and increased thermal stability of GAM15 is also discussed. 相似文献
945.
Abdul KHALIQ Muhammad ASHFAQ Waseem AKRAM Jhong Kyoung CHOI Jong-Jin LEE 《Entomological Research》2005,35(3):153-160
Sugarcane (Saccharum officinarum L.) varieties CP‐43/33 and L‐118 susceptible, BF‐162 and SPSG‐26 resistant while CP‐72/2086 as intermediate were screened for studies on top borer, Scirpophaga nivella Fabricus (Pyralidae: Lepidoptera). Morpho‐physio chemical plant factors as well as quality of sugar were examined to elucidate the relationship between pest infestations. The observations on leaf thickness 0.735* and moisture contents 0.771* showed positive and significant correlation with the pest infestation at tillering stage. Total minerals, manganese and copper contents did not show significant correlation with the pest infestation, whereas nitrogen, potassium, calcium, magnesium and ferrous contents manifested positive and significant correlation with the pest infestation. Phosphorous, carbohydrates, fats and zinc produced significant and adverse effect on the pest infestation at tillering stage. Zinc contents with contrasting behaviors appeared to be the most important character with co‐efficient value of 0.764 followed by ferrous with positive sign. The effect of borer infestation was significantly negative on pol (sucrose), Brix contents (total soluble solids), and CCS (commercial cane sugar). The coefficient of determination value was 0.821, obtained by computing fiber content, pol, Brix and CCS factors together for multivariate regression models. Application of trash mulching at the time of sowing proved to be the most effective treatment with minimum infestation (3.91%) of borer and maximum protection level (62.87%) followed by Furadan®, removal of dead hearts + spike thrust, hand collection of egg masses, and cutting of shoots at 15 days interval. 相似文献
946.
Zhenxing Feng Xiuzhen Hu Zhuo Jiang Hangyu Song Muhammad Aqeel Ashraf 《Saudi Journal of Biological Sciences》2016,23(2):189-197
The recognition of protein folds is an important step in the prediction of protein structure and function. Recently, an increasing number of researchers have sought to improve the methods for protein fold recognition. Following the construction of a dataset consisting of 27 protein fold classes by Ding and Dubchak in 2001, prediction algorithms, parameters and the construction of new datasets have improved for the prediction of protein folds. In this study, we reorganized a dataset consisting of 76-fold classes constructed by Liu et al. and used the values of the increment of diversity, average chemical shifts of secondary structure elements and secondary structure motifs as feature parameters in the recognition of multi-class protein folds. With the combined feature vector as the input parameter for the Random Forests algorithm and ensemble classification strategy, we propose a novel method to identify the 76 protein fold classes. The overall accuracy of the test dataset using an independent test was 66.69%; when the training and test sets were combined, with 5-fold cross-validation, the overall accuracy was 73.43%. This method was further used to predict the test dataset and the corresponding structural classification of the first 27-protein fold class dataset, resulting in overall accuracies of 79.66% and 93.40%, respectively. Moreover, when the training set and test sets were combined, the accuracy using 5-fold cross-validation was 81.21%. Additionally, this approach resulted in improved prediction results using the 27-protein fold class dataset constructed by Ding and Dubchak. 相似文献
947.
P. Zhao Y. Wang Y. Zhang T. Guo Z. Zhang W.J. Zhang X.G. Zhang Muhammad Aqeel Ashraf 《Saudi Journal of Biological Sciences》2016,23(3):353-357
In this study, the selenium enriched peanuts and the different solubility proteins extracted from them were investigated. The dried defatted selenium enriched peanuts (SeP) powder (0.3147 μg/g) had a 2.5-fold higher mean total selenium concentration than general peanuts (GP) power (0.1233 μg/g). The SeP had higher concentration of selenium, manganese and zinc than that of GP, but less calcium. The rate of extraction of protein was 23.39% for peanuts and alkali soluble protein was the main component of protein in SeP, which accounted for 92.82% of total soluble protein and combined selenium was 77.33% of total selenium protein. In different forms of proteins from SeP, the WSePr due to higher concentration of selenium had higher DPPH free-radical scavenging activity, higher reducing activity and longer induction time than other proteins. 相似文献
948.
Bin Zheng Gaoyang Xing Ye Bi Guodong Yan Jing Wang Yingkun Cheng Yan Liu Muhammad Aqeel Ashraf Jing Xie 《Saudi Journal of Biological Sciences》2016,23(1):54-65
As a novel oral drug delivery system, proliposome was applied to improve the solubility of active components of Ginkgo biloba extract (GbE). There are currently few reports focusing on the pharmacokinetic characteristics of proliposome of GbE (GbP). A rapid and sensitive ultra performance liquid chromatography–tandem mass spectrometry (UPLC–MS/MS) method for the simultaneous quantification of active components of GbP and a commercial tablet product (Ginaton) in rat plasma was developed and successfully validated. The method was applied to the comparative pharmacokinetic evaluation of GbP and Ginaton in rat plasma. The results indicated that GbP has a significant effect on absorption, elimination and bioavailability of flavonoids and terpenoid lactones in comparison with Ginaton. The obtained results would be helpful for evaluating the absorption mechanism in the gastrointestinal tract in pharmacokinetic level and guiding the development of the novel oral drug delivery system. 相似文献
949.
Improving magnesium uptake,photosynthesis and antioxidant enzyme activities of watermelon by grafting onto pumpkin rootstock under low magnesium 总被引:1,自引:0,他引:1
Yuan Huang Yanyan Jiao Muhammad Azher Nawaz Chen Chen Li Liu Zhen Lu Qiusheng Kong Fei Cheng Zhilong Bie 《Plant and Soil》2016,398(1-2):229-241