全文获取类型
收费全文 | 4175篇 |
免费 | 322篇 |
国内免费 | 1篇 |
专业分类
4498篇 |
出版年
2022年 | 55篇 |
2021年 | 83篇 |
2020年 | 45篇 |
2019年 | 49篇 |
2018年 | 83篇 |
2017年 | 65篇 |
2016年 | 113篇 |
2015年 | 127篇 |
2014年 | 213篇 |
2013年 | 232篇 |
2012年 | 267篇 |
2011年 | 262篇 |
2010年 | 169篇 |
2009年 | 140篇 |
2008年 | 213篇 |
2007年 | 186篇 |
2006年 | 200篇 |
2005年 | 174篇 |
2004年 | 157篇 |
2003年 | 133篇 |
2002年 | 111篇 |
2001年 | 119篇 |
2000年 | 83篇 |
1999年 | 82篇 |
1998年 | 40篇 |
1997年 | 31篇 |
1996年 | 31篇 |
1995年 | 33篇 |
1994年 | 38篇 |
1993年 | 35篇 |
1992年 | 65篇 |
1991年 | 61篇 |
1990年 | 60篇 |
1989年 | 47篇 |
1988年 | 40篇 |
1987年 | 52篇 |
1986年 | 40篇 |
1985年 | 47篇 |
1984年 | 45篇 |
1983年 | 33篇 |
1982年 | 34篇 |
1981年 | 23篇 |
1979年 | 31篇 |
1978年 | 22篇 |
1977年 | 33篇 |
1975年 | 25篇 |
1973年 | 24篇 |
1972年 | 22篇 |
1969年 | 30篇 |
1967年 | 19篇 |
排序方式: 共有4498条查询结果,搜索用时 31 毫秒
231.
Early investigators reported the occurrence of unidentified protein factors in biological fluids that may regulate sperm motility essential for fertility potential. This study reports for the first time purification of a forward motility stimulating protein (FMSF-I), to apparent homogeneity, from a biological fluid (buffalo blood serum) and its characterization. FMSF-I is the major motility protein of buffalo serum: a rich source of the factor. FMSF showed high protein specificity and affinity for activating forward motility of goat cauda epididymal spermatozoa. The motility promoter at 0.5 microM level showed maximal activity when nearly 60%-70% of spermatozoa expressed forward motility. It is a 66 kDa monomeric acidic protein rich in aspartate, glutamate, and leucine with isoelectric point of 3.7. FMSF: a Mg2+ -dependent protein binds to concanavalin A-agarose and the glycoprotein nature of FMSF has been confirmed by PAS staining. The factor lost activity completely when treated with alpha-mannosidase showing that the sugar part of the protein is essential for its biological activity. FMSF has no species specificity for its motility-activating potential. Sperm surface has specific receptors of FMSF, which is strongly immunogenic. The factor is present in testis and epididymis although liver is its richest source. Motility promoting efficacy of FMSF is markedly higher than the well-known non-protein motility activators: theophylline and bicarbonate or their combination. FMSF is a physiological activator of sperm motility and as a slaughterhouse byproduct it has potentiality for solving some of the problems of animal breeding, conservation of endangered species, and human infertility: a global social problem. 相似文献
232.
Summary Two species of fungi,Tryblidiella rufula (Spreng.)Sacc. andTrabutia butleri
Theiss &Syd. have been figured and described for the first time from Orissa. The former was found growing on dead twigs ofCitrus aurantifolia (Christm.)Swingle and onCitrus sp. and the latter on living leaves ofFicus religiosa L. 相似文献
233.
Tripti Sharma Pradip Kumar Das Probal Ranjan Ghosh Dipak Banerjee Bikash Chandra Das 《Biological Rhythm Research》2016,47(4):519-527
In vitro activity of milk leukocytes (viz. neutrophils, lymphocytes and macrophages) was evaluated in forty-eight (48) clinically healthy high-yielding cross-bred cows of mid-lactation stage (100–200 days of lactation), divided into four groups namely 1st parity (n = 12), 2nd parity (n = 12), 3rd parity (n = 12) and 4th and above parity (n = 12). Milk samples were taken (250 ml/cow) were taken. Milk somatic cell counts (SCC) and differential leukocyte counts (DLC) were performed microscopically. In vitro phagocytic index (PI) of milk neutrophils and macrophages was evaluated by colorimetric nitro blue tetrazolium reductive assay. Mitogen-induced milk lymphocyte blastogenic response was measured by colorimetric MTT (tetrazolium) assay after isolation of the milk leukocytes by density gradient centrifugation. Milk SCC differed significantly (p < 0.01) between different parity. Cows of 4 and above parity showed significantly (p < 0.01) higher milk SCC compared to primiparous cows. There was no significant difference in milk DLC during different parities in high-yielding cross-bred cows. There was a significant (p < 0.01) variation in lymphocyte blastogenesis amongst parity. The highest value of lymphocyte blastogenesis was seen at 3rd parity, whereas lowest value was obtained in the cows of both 1st and 4th or above parity. PI of milk neutrophils did not differ significantly between parity. PI of milk macrophages was significantly (p < 0.01) higher in 3rd parity and lower (p < 0.01) in 1st and 4th parities. The study indicated that depressed activity of milk lymphocytes and macropages was lower and SCC was higher in the cows of 4th and above parity indicating more mammary stress and hence susceptible to udder infection and mastitis. Therefore, better care and managemental interventions should be taken around these periods. 相似文献
234.
Kezhavituo Vupru Joydip Mukherjee Dipak Banerjee P. Perumal Prabal Ranjan Ghosh 《Biological Rhythm Research》2016,47(6):841-850
The role of lactogenic hormones (prolactin, growth hormone, cortisol and thyroid hormone) on lactation yield in Mithun cows as well as their rhythmicity throughout the lactation cycle were studied in Mizoram (n = 4) and Nagaland (n = 7) strain of mithun (Bos frontalis). Blood samples were collected from all the animals from the day of calving to the complete dry off at an interval of 15 days. All the hormones were estimated in the serum by commercially available ELISA kits. Plasma level of cortisol (μg/dl), growth hormone (GH, in ng/ml), prolactin (PRL, in μIU/ml), triiodothyronine (T3, in nmol/μl) and thyroxin (T4, in ng/ml) were 20.84 ± 0.29, 28.08 ± 0.56, 9.87 ± 0.20, 27.82 ± 0.56 and 51.33 ± 0.48, respectively, in mithun irrespective of strains during the lactation period. Levels of all the hormones varied significantly (p ≤ 0.01) during different days of lactation cycle but, there was no significant difference among strain. Levels of PRL, GH, cortisol and T3 were significantly (p < 0.01) higher around calving and declined sharply. The hormones remained in almost steady state during mid-lactation and declined during late lactation. All the hormones stated above were positively correlated with lactational yield thus their role on lactogenesis and galactopoiesis was established. 相似文献
235.
236.
237.
Apoptosis Induced by Infection of Primary Brain Cultures with Diverse Human Immunodeficiency Virus Type 1 Isolates: Evidence for a Role of the Envelope 总被引:5,自引:3,他引:5 下载免费PDF全文
Asa Ohagen Sajal Ghosh Jianglin He Karen Huang Youzhi Chen Menglan Yuan Rapin Osathanondh Suzanne Gartner Bin Shi George Shaw Dana Gabuzda 《Journal of virology》1999,73(2):897-906
Apoptosis of neurons and astrocytes is induced by human immunodeficiency type 1 (HIV-1) infection in vitro and has been demonstrated in brain tissue from patients with AIDS. We analyzed a panel of diverse HIV-1 primary isolates for the ability to replicate and induce neuronal and astrocyte apoptosis in primary human brain cultures. Apoptosis was induced three- to eightfold by infection with the blood-derived HIV-1 isolates 89.6, SG3, and ADA. In contrast, the brain-derived HIV-1 isolates YU2, JRFL, DS-br, RC-br, and KJ-br did not induce significant levels of apoptosis. The ability of HIV-1 isolates to induce apoptosis was independent of their replication capacity. Studies of recombinant chimeras between the SG3 and YU2 viruses showed that replacement of the YU2 Env with the SG3 Env was sufficient to confer the ability to induce apoptosis to the YU2 virus. Replacement of the Env V3 regions alone largely conferred the phenotypes of the parental clones. The SG3 Env used CXCR4 and CCR3 as coreceptors for virus entry, whereas YU2 used CCR5 and CCR3. The V3 regions of SG3 and YU2 conferred the ability to use CXCR4 and CCR5, respectively. In contrast, the 3′ region of Env, particularly the C3V4 region, was required in conjunction with the V3 region for efficient use of CCR3. These results provide evidence that Env is a major determinant of neurodegenerative mechanisms associated with HIV-1 infection in vitro and raise the possibility that blood-derived viruses which emerge during the late stages of disease may affect disease progression in the central nervous system. 相似文献
238.
Identification of a phosphoenolpyruvate:fructose 1-phosphotransferase system in Azospirillum brasilense 总被引:3,自引:4,他引:3 下载免费PDF全文
An inducible phosphoenolpyruvate:fructose phosphotransferase system has been detected in Azospirillum brasilense, which requires a minimum of two components of the crude extracts for activity: (i) a soluble fraction (enzyme I) and (ii) a membrane fraction (enzyme II). The uninduced cells neither show any uptake of fructose nor express activity of either of these two enzyme fractions. C-1 of fructose is the site of phosphorylation. This phosphotransferase system does not accept glucose as a substrate for phosphorylation. 相似文献
239.
P. C. Ghosh 《Plant and Soil》1966,25(1):65-72
Summary The total nitrogen uptake of wheat in a pot experiment was found to be linearly related to the amounts of applied nitrogen in the range of 0 to 120 pounds N per acre. The N-value of the soil used in the pot experiment was estimated by extrapolation of the regression line of total nitrogen uptakevs rates of added nitrogen. The N-value was compared with the values of available soil nitrogen as estimated by three chemical methods, two of which used alkaline KMnO4 and the third, dilute H2SO4 as hydrolysing agents of soil organic nitrogen. Results obtained by none of these methods agreed closely with the N-value. The amounts of nitrogen estimated by Shihata's method and Purvis and Leo's method were practically same and were appreciably lower than N-value whereas the value obtained by Subbiah and Asija's method was much higher than the N-value. However, Purvis and Leo's method deserves further study as it is well suited for mass-scale analysis. 相似文献
240.
Triplet-state energies, zero-field splittings (ZFS), and total decay rate constants of the individual triplet-state sublevels of the tryptophan (Trp) residues located at positions 126, 138, and 158 in bacteriophage T4 lysozyme have been determined by using low-temperature phosphorescence and optical detection of magnetic resonance spectroscopy in zero applied magnetic field. An investigation of spectral and kinetic properties of individual Trp residues was facilitated by measurements on point-mutated proteins containing two Trp----Tyr substitutions. We find that the phosphorescence lifetime of the buried Trp-138 is considerably shorter than those of the solvent-exposed Trp residues. CH3HgII binding to cysteine residues in T4 lysozyme selectively perturbs the triplet state of Trp-158 by means of an external heavy-atom effect. In contrast with the previous observation of selective x-sublevel perturbation in the Trp-CH3Hg complex, the radiative character of the z sublevel (z is the out-of-plane axis) is selectively enhanced due to the heavy-atom perturbation of Trp-158. The observed pattern of radiative and total sublevel decay constants of the perturbed Trp is attributed to a special orientation of the Hg atom with respect to the indole plane. 相似文献