全文获取类型
收费全文 | 2162篇 |
免费 | 96篇 |
专业分类
2258篇 |
出版年
2023年 | 21篇 |
2022年 | 32篇 |
2021年 | 49篇 |
2020年 | 31篇 |
2019年 | 37篇 |
2018年 | 68篇 |
2017年 | 47篇 |
2016年 | 52篇 |
2015年 | 90篇 |
2014年 | 113篇 |
2013年 | 152篇 |
2012年 | 179篇 |
2011年 | 131篇 |
2010年 | 95篇 |
2009年 | 95篇 |
2008年 | 128篇 |
2007年 | 91篇 |
2006年 | 93篇 |
2005年 | 93篇 |
2004年 | 78篇 |
2003年 | 83篇 |
2002年 | 67篇 |
2001年 | 38篇 |
2000年 | 39篇 |
1999年 | 33篇 |
1998年 | 14篇 |
1997年 | 8篇 |
1996年 | 8篇 |
1995年 | 16篇 |
1994年 | 7篇 |
1993年 | 13篇 |
1992年 | 16篇 |
1991年 | 18篇 |
1990年 | 21篇 |
1989年 | 25篇 |
1988年 | 17篇 |
1987年 | 19篇 |
1986年 | 24篇 |
1985年 | 11篇 |
1984年 | 7篇 |
1983年 | 11篇 |
1982年 | 6篇 |
1981年 | 17篇 |
1980年 | 12篇 |
1979年 | 6篇 |
1977年 | 8篇 |
1974年 | 5篇 |
1973年 | 4篇 |
1972年 | 4篇 |
1969年 | 6篇 |
排序方式: 共有2258条查询结果,搜索用时 0 毫秒
41.
Suresh Babu K Tiwari AK Srinivas PV Ali AZ China Raju B Rao JM 《Bioorganic & medicinal chemistry letters》2004,14(14):3841-3845
The methanolic extract of rhizome of Himalayan rhubarb Rheum emodi displayed mild yeast as well as mammalian intestinal alpha-glucosidase inhibitory activity. However, further fractionation of active extract led to the isolation of several potent molecules in excellent yields, displaying varying degrees of inhibition on two test models of alpha-glucosidase. Rhapontigenin, desoxyrhapontigenin, chrysophanol-8-O-beta-d-glucopyranoside, torachrysone-8-O-beta-d-glucopyranoside displayed potent yeast alpha-glucosidase inhibition. However chrysophanol-8-O-beta-d-glucopyranoside, desoxyrhaponticin and torachrysone-8-O-beta-d-glucopyranoside displayed potent to moderate mammalian alpha-glucosidase inhibitory activity. Other compounds displayed mild activity on both the tests. Except desoxyrhapontigenin and rhapontigenin that increased Vmax, other compounds including crude extract decreased the Vmax significantly (p<0.02) in yeast alpha-glucosidase test. Further kinetic analysis on mammalian alpha-glucosidase inhibition showed that chrysophanol-8-O-beta-d-glucopyranoside, desoxyrhaponticin and torachrysone-8-O-beta-d-glucopyranoside may be classified as mixed-noncompetitive inhibitors. However, desoxyrhapontigenin and rhapontigenin may be classified as modulators of enzyme activity. Presence and position of glycoside moiety in compounds appear important for better inhibition of mammalian alpha-glucosidase. This is the first report assigning particularly, mammalian intestinal alpha-glucosidase inhibitory activity to these compounds. Chrysophanol-8-O-beta-d-glucopyranoside, desoxyrhaponticin, desoxyrhapontigenin and rhapontigenin have been isolated in substantial yields from R. emodi for the first time. Therefore, these compounds may have value in the treatment and prevention of hyperglycemia associated diabetes mellitus. 相似文献
42.
J Crossa P Pérez J Hickey J Burgue?o L Ornella J Cerón-Rojas X Zhang S Dreisigacker R Babu Y Li D Bonnett K Mathews 《Heredity》2014,112(1):48-60
Genomic selection (GS) has been implemented in animal and plant species, and is regarded as a useful tool for accelerating genetic gains. Varying levels of genomic prediction accuracy have been obtained in plants, depending on the prediction problem assessed and on several other factors, such as trait heritability, the relationship between the individuals to be predicted and those used to train the models for prediction, number of markers, sample size and genotype × environment interaction (GE). The main objective of this article is to describe the results of genomic prediction in International Maize and Wheat Improvement Center''s (CIMMYT''s) maize and wheat breeding programs, from the initial assessment of the predictive ability of different models using pedigree and marker information to the present, when methods for implementing GS in practical global maize and wheat breeding programs are being studied and investigated. Results show that pedigree (population structure) accounts for a sizeable proportion of the prediction accuracy when a global population is the prediction problem to be assessed. However, when the prediction uses unrelated populations to train the prediction equations, prediction accuracy becomes negligible. When genomic prediction includes modeling GE, an increase in prediction accuracy can be achieved by borrowing information from correlated environments. Several questions on how to incorporate GS into CIMMYT''s maize and wheat programs remain unanswered and subject to further investigation, for example, prediction within and between related bi-parental crosses. Further research on the quantification of breeding value components for GS in plant breeding populations is required. 相似文献
43.
G. V. Chowdary S. Hari Krishna G. Hanumantha Rao 《Bioprocess and biosystems engineering》2000,23(6):681-685
Amyloglucosidase (EC 3.2.1.3) from Aspergillus niger was employed for the saccharification of mango (Mangifera indica Linn) kernel starch. Response surface methodology based on a three-level three-factor Box-Behnken design was employed to optimize the important process variables such as substrate concentration (137.5-412.5 mg), enzyme concentration (4-12 mg) and temperature (35-55 °C). The sugar yield increased with both enzyme concentration and temperature, and decreased with substrate concentration. The response surface model indicated optimum conditions (substrate, 137.5 mg; enzyme, 12 mg; temperature, 55 °C) for obtaining 0.4851 mg sugar/mg substrate, which was also verified experimentally. 相似文献
44.
Masuku SM Babu D Martin EM Koo OK O'Bryan CA Crandall PG Ricke SC 《Journal of applied microbiology》2012,113(1):89-95
Aims: To test the efficacy of four wipe cloth types (cotton bar towel, nonwoven, microfibre and blended cellulose/cotton) with either quaternary ammonia cleaning solution or silver dihydrogen citrate (SDC) in cleaning food contact surfaces. Methods: Swab samples collected from untreated, cloth‐treated and cloth disinfectant‐treated surfaces were subjected to hygiene monitoring using adenosine triphosphate (ATP) bioluminescence and aerobic total plate counting (TPC) assays. Results: Adenosine triphosphate measurements taken after wiping the surfaces showed poor cleaning by nonwoven cloths (2·89 RLU 100 cm?2) than the microfibre (2·30 RLU 100 cm?2), cotton terry bar (2·26 RLU 100 cm?2) and blended cellulose/cotton cloth types (2·20 RLU 100 cm?2). The cellulose/cotton cloth showed highest log reduction in ATP‐B RLU values (95%) and CFU values (98·03%) when used in combination with SDC disinfectant. Conclusions: Cleaning effect of wiping cloths on food contact surfaces can be enhanced by dipping them in SDC disinfectant. ATP‐B measurements can be used for real‐time hygiene monitoring in public sector, and testing microbial contamination provides more reliable measure of cleanliness. Significance and Impact of the Study: Contaminated food contact surfaces need regular hygiene monitoring. This study could help to estimate and establish contamination thresholds for surfaces at public sector facilities and to base the effectiveness of cleaning methods. 相似文献
45.
Pandey Abhay K. Deka Bhabesh Varshney Richa Cheramgoi Evelyn Chepkirui Babu Azariah 《BioControl》2021,66(4):445-462
BioControl - In recent years, Fungal Biocontrol Agents (FBCAs) have played a significant role in the biological control of pests and plant pathogens of several economically important crops,... 相似文献
46.
S. Hari Krishna K. C. Sekhar Rao J. Suresh Babu D. Srirami Reddy S. Hari Krishna 《Bioprocess and biosystems engineering》2000,22(5):467-470
High yielding mutant strain, Trichoderma reesei QM-9414, was employed for the cellulase enzyme production. Enzyme production conditions (pH, inoculum age and concentration, and organic supplements) were optimized. The ability of partially purified enzyme to hydrolyze various regionally abundant lignocellulosic raw materials was studied. Enzymatic hydrolysis conditions (temperature, pH, enzyme and substrate concentrations) were optimized. Temperature 50v°C, pH 4.5, enzyme concentration 40 FPU/g substrate and substrate concentration 2.5% were found to be optimum for the maximum yields of sugars. #-glucosidase supplementation was found to increase both the sugar yield and hydrolysis rate, and shorten the reaction time significantly. 相似文献
47.
Hari Ji Singh Nand Kishor Gour Pradeep Kumar Rao Laxmi Tiwari 《Journal of molecular modeling》2013,19(11):4815-4822
The present work deals with the theoretical investigation on the Cl initiated H-atom abstraction reaction of sevoflurane, (CF3)2CHOCH2F. A dual-level procedure has been adopted for studying the kinetics of the reaction. Geometrical optimization and frequency calculation were performed at DFT(BHandHLYP)/6-311G(d,p) while single-point energy calculation was made at CCSD(T)/6-311G(d,p) level of theory. The intrinsic reaction coordinate (IRC) calculation has also been performed to confirm the smooth transition from the reactant to product through the respective transition state. The rate constants were calculated using conventional transition state theory (TST). It has been found that 99 % of the reaction proceeded via the H-atom abstraction from the –CH2F end of the sevoflurane. The rate constant of the dominant path is found to be 1.13 × 10?13 cm3 molecule?1 s?1. This is in excellent agreement with the reported experimental rate constant of 1.10 × 10?13 cm3 molecule?1 s?1 obtained by relative rate method using FTIR/Smog chamber and LP/LIF techniques. 相似文献
48.
Smitha Surendran Thamarath A. Alia Esha Roy Karthick Babu Sai Sankar Gupta John H. Golbeck Jörg Matysik 《Photosynthesis research》2013,117(1-3):461-469
The solid-state photo-CIDNP (photochemically induced dynamic nuclear polarization) effect is studied in photosynthetic reaction centers of Heliobacillus mobilis at different magnetic fields by 13C MAS (magic-angle spinning) NMR spectroscopy. Two active states of heliobacterial reaction centers are probed: an anaerobic preparation of heliochromatophores (“Braunstoff”, German for “brown substance”) as well as a preparation of cells after exposure to oxygen (“Grünstoff”, “green substance”). Braunstoff shows significant increase of enhanced absorptive (positive) signals toward lower magnetic fields, which is interpreted in terms of an enhanced differential relaxation (DR) mechanism. In Grünstoff, the signals remain emissive (negative) at two fields, confirming that the influence of the DR mechanism is comparably low. 相似文献
49.
Roshan Joy Martis U. Rajendra Acharya Hari Prasad Chua Kuang Chua Choo Min Lim Jasjit S. Suri 《Biomedical signal processing and control》2013,8(6):888-900
Atrial fibrillation (AF) and atrial flutter (AFL) are the two common atrial arrhythmia encountered in the clinical practice. In order to diagnose these abnormalities the electrocardiogram (ECG) is widely used. The conventional linear time and frequency domain methods cannot decipher the hidden complexity present in these signals. The ECG is inherently a non-linear, non-stationary and non-Gaussian signal. The non-linear models can provide improved results and capture minute variations present in the time series. Higher order spectra (HOS) is a non-linear dynamical method which is highly rugged to noise. In the present study, the performances of two methods are compared: (i) 3rd order HOS cumulants and (ii) HOS bispectrum. The 3rd order cumulant and bispectrum coefficients are subjected to dimensionality reduction using independent component analysis (ICA) and classified using classification and regression tree (CART), random forest (RF), artificial neural network (ANN) and k-nearest neighbor (KNN) classifiers to select the best classifier. The ICA components of cumulant coefficients have provided the average accuracy, sensitivity, specificity and positive predictive value of 99.50%, 100%, 99.22% and 99.72% respectively using KNN classifier. Similarly, the ICA components of HOS bispectrum coefficients have yielded the average accuracy, sensitivity, specificity and PPV of 97.65%, 98.16%, 98.75% and 99.53% respectively using KNN. So, the ICA performed on the 3rd order HOS cumulants coupled with KNN classifier performed better than the HOS bispectrum method. The proposed methodology is robust and can be used in mass screening of cardiac patients. 相似文献
50.
A. M. Babu N. B. Chowdary V. Kumar M. V. Rajan S. B. Dandin 《Archives Of Phytopathology And Plant Protection》2013,46(4):290-295
Abstract The pre-penetration and infection process of Colletotrichum dematium on mulberry leaf was investigated by scanning electron microscope. Conidia produced on germination appressoria directly or at the end of short germ tubes. Appressoria were formed mostly over cuticle, but sometimes over stomata also. At 72 h post-inoculation, an extensive network of sub-cuticular runner hyphae (RH) was produced. The RH were traceable by the cuticular bulgings on leaf surface. The RH emerged to leaf surface through ruptured cuticle to form secondary infection hyphae (SIH). The SIH re-entered the leaf tissue by sending penetration branches through stomata. Conidia were formed singly on short conidiophores from the RH and SIH, at short intervals. The conidia developed on RH were exposed to leaf surface through ruptured cuticle. Some times conidia were released through stomata also. The RH and SIH had thick knots from which hyphal branches and conidia were developed. Definite acervuli were not developed. 相似文献