全文获取类型
收费全文 | 3538篇 |
免费 | 197篇 |
专业分类
3735篇 |
出版年
2022年 | 33篇 |
2021年 | 71篇 |
2020年 | 34篇 |
2019年 | 52篇 |
2018年 | 58篇 |
2017年 | 67篇 |
2016年 | 86篇 |
2015年 | 120篇 |
2014年 | 134篇 |
2013年 | 174篇 |
2012年 | 237篇 |
2011年 | 200篇 |
2010年 | 134篇 |
2009年 | 114篇 |
2008年 | 160篇 |
2007年 | 131篇 |
2006年 | 123篇 |
2005年 | 113篇 |
2004年 | 108篇 |
2003年 | 76篇 |
2002年 | 85篇 |
2001年 | 91篇 |
2000年 | 63篇 |
1999年 | 70篇 |
1998年 | 34篇 |
1997年 | 29篇 |
1996年 | 27篇 |
1995年 | 26篇 |
1992年 | 55篇 |
1991年 | 63篇 |
1990年 | 46篇 |
1989年 | 56篇 |
1988年 | 39篇 |
1987年 | 48篇 |
1986年 | 31篇 |
1985年 | 73篇 |
1984年 | 47篇 |
1983年 | 51篇 |
1982年 | 26篇 |
1981年 | 30篇 |
1980年 | 41篇 |
1979年 | 53篇 |
1978年 | 33篇 |
1976年 | 25篇 |
1975年 | 27篇 |
1974年 | 32篇 |
1973年 | 28篇 |
1971年 | 34篇 |
1970年 | 29篇 |
1969年 | 33篇 |
排序方式: 共有3735条查询结果,搜索用时 14 毫秒
101.
Claire L. Gibson Kirtiman Srivastava Nikola Sprigg Philip M. W. Bath Ulvi Bayraktutan 《Journal of neurochemistry》2014,129(5):816-826
Ischaemic strokes evoke blood–brain barrier (BBB) disruption and oedema formation through a series of mechanisms involving Rho‐kinase activation. Using an animal model of human focal cerebral ischaemia, this study assessed and confirmed the therapeutic potential of Rho‐kinase inhibition during the acute phase of stroke by displaying significantly improved functional outcome and reduced cerebral lesion and oedema volumes in fasudil‐ versus vehicle‐treated animals. Analyses of ipsilateral and contralateral brain samples obtained from mice treated with vehicle or fasudil at the onset of reperfusion plus 4 h post‐ischaemia or 4 h post‐ischaemia alone revealed these benefits to be independent of changes in the activity and expressions of oxidative stress‐ and tight junction‐related parameters. However, closer scrutiny of the same parameters in brain microvascular endothelial cells subjected to oxygen–glucose deprivation ± reperfusion revealed marked increases in prooxidant NADPH oxidase enzyme activity, superoxide anion release and in expressions of antioxidant enzyme catalase and tight junction protein claudin‐5. Cotreatment of cells with Y‐27632 prevented all of these changes and protected in vitro barrier integrity and function. These findings suggest that inhibition of Rho‐kinase after acute ischaemic attacks improves cerebral integrity and function through regulation of endothelial cell oxidative stress and reorganization of intercellular junctions.
102.
103.
Priyanka Dhar Vijay K. Sharma Kalpana B. Hota Saroj K. Das Sunil K. Hota Ravi B. Srivastava Shashi B. Singh 《PloS one》2014,9(1)
Acute exposure to hypobaric hypoxia at high altitude is reported to cause sympathetic dominance that may contribute to the pathophysiology of high altitude illnesses. The effect of prolonged stay at high altitude on autonomic functions, however, remains to be explored. Thus, the present study aimed at investigating the effect of high altitude on autonomic neural control of cardiovascular responses by monitoring heart rate variability (HRV) during chronic hypobaric hypoxia. Baseline electrocardiography (ECG) data was acquired from the volunteers at mean sea level (MSL) (<250 m) in Rajasthan. Following induction of the study population to high altitude (4500–4800 m) in Ladakh region, ECG data was acquired from the volunteers after 6 months (ALL 6) and 18 months of induction (ALL 18). Out of 159 volunteers who underwent complete investigation during acquisition of baseline data, we have only included the data of 104 volunteers who constantly stayed at high altitude for 18 months to complete the final follow up after 18 months. HRV parameters, physiological indices and biochemical changes in serum were investigated. Our results show sympathetic hyperactivation along with compromise in parasympathetic activity in ALL 6 and ALL 18 when compared to baseline data. Reduction of sympathetic activity and increased parasympathetic response was however observed in ALL 18 when compared to ALL 6. Our findings suggest that autonomic response is regulated by two distinct mechanisms in the ALL 6 and ALL 18. While the autonomic alterations in the ALL 6 group could be attributed to increased sympathetic activity resulting from increased plasma catecholamine concentration, the sympathetic activity in ALL 18 group is associated with increased concentration of serum coronary risk factors and elevated homocysteine. These findings have important clinical implications in assessment of susceptibility to cardio-vascular risks in acclimatized lowlanders staying for prolonged duration at high altitude. 相似文献
104.
Effects of elevated CO<Subscript>2</Subscript> and nitrogen on wheat growth and photosynthesis 总被引:1,自引:0,他引:1
M.?PalEmail author L.?S.?Rao V.?Jain A.?C.?Srivastava R.?Pandey A.?Raj K.?P.?Singh 《Biologia Plantarum》2005,49(3):467-470
The effects of nitrogen [75 and 150 kg (N) ha−1] and elevated CO2 on growth, photosynthetic rate, contents of soluble leaf proteins and activities of ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) and nitrate reductase (NR) were studied on wheat (Triticum aestivum L. cv. HD-2285) grown in open top chambers under either ambient (AC) or elevated (EC) CO2 concentration (350 ± 50, 600 ± 50 μmol mol−1) and analyzed at 40, 60 and 90 d after sowing. Plants grown under EC showed greater photosynthetic rate and were taller and attained greater leaf area along with higher total plant dry mass at all growth stages than those grown under AC. Total soluble and Rubisco protein contents decreased under EC but the activation of Rubisco was higher at EC with higher N supply. Nitrogen increased the NR activity whereas EC reduced it. Thus, EC causes increased growth and PN ability per unit uptake of N in wheat plants, even if N is limiting. 相似文献
105.
Diethylcarbamazine (DEC) reacted with liver cell plasma membrane of rodent hosts-cotton rat, albino rat and Mastomys natalensis exhibiting the presence of both saturable and unsaturable components. The presence of lectins or sugar derivatives did not affect the binding significantly. The drug showed similar binding pattern with serum but the saturation was reached at a much lower concentration of the ligand. Data obtained with a variety of macromolecules, particularly with the homopolymers of amino acids indicate that DEC does not require any specific constituent of the membrane for binding. The nonspecific nature of DEC binding does not provide any convincing clue for the accumulation of microfilariae specifically in the liver following the drug treatment. 相似文献
106.
Nikhil M. Vad Prabodh K. Kandala Sanjay K. Srivastava Majid Y. Moridani 《Chemico-biological interactions》2010,183(3):462-471
The aim of this study was to identify a phenolic prodrug compound that is minimally metabolized by rat liver microsomes, but yet could form quinone reactive intermediates in melanoma cells as a result of its bioactivation by tyrosinase. In current work, we investigated 24 phenolic compounds for their metabolism by tyrosinase, rat liver microsomes and their toxicity towards murine B16-F0 and human SK-MEL-28 melanoma cells. A linear correlation was found between toxicities of phenolic analogs towards SK-MEL-28 and B16-F0 melanoma cells, suggesting similar mechanisms of toxicity in both cell lines. 4-HEB was identified as the lead compound. 4-HEB (IC50 48 h, 75 μM) showed selective toxicity towards five melanocytic melanoma cell lines SK-MEL-28, SK-MEL-5, MeWo, B16-F0 and B16-F10, which express functional tyrosinase, compared to four non-melanoma cells lines SW-620, Saos-2, PC3 and BJ cells and two amelanotic SK-MEL-24, C32 cells, which do not express functional tyrosinase. 4-HEB caused significant intracellular GSH depletion, ROS formation, and showed significantly less toxicity to tyrosinase specific shRNA transfected SK-MEL-28 cells. Our findings suggest that presence of a phenolic group in 4-HEB is critical for its selective toxicity towards melanoma cells. 相似文献
107.
Prejwltta Maurya Preeti Sharma Lalit Mohan Lata Batabyal C.N. Srivastava 《Journal of Asia》2009,12(2):113-115
The larvicidal effect of the crude carbon tetrachloride, methanol and petroleum ether leaf extracts of a widely grown medicinal plant, Ocimum basilicum, against Anopheles stephensi and Culex quinquefasciatus was evaluated. Petroleum ether extract was found to be the most effective against the larvae of both mosquitoes, with LC50 values of 8.29, 4.57; 87.68, 47.25 ppm and LC90 values of 10.06, 6.06; 129.32, 65.58 ppm against A. stephensi and C. quinquefasciatus being observed after 24 and 48 h of treatment, respectively. The efficacy of petroleum ether was followed by that of the carbon tetrachloride and methanol extracts, which had LC50 values of 268.61, 143.85; 446.61, 384.84 ppm and LC90 values of 641.23, 507.80; 923.60, 887.00 ppm against A. stephensi after 24 and 48 h, respectively, and LC50 values of 24.14, 17.02; 63.48, 53.77 ppm and LC90 values of 295.38, 204.23; 689.71, 388.87 ppm against C. quinquefasciatus after 24 and 48 h of treatment, respectively. These extracts are highly toxic against mosquito larvae from a range of species; therefore, they may be useful for the management of mosquito larvae to control vector borne diseases. 相似文献
108.
109.
Pratibha Misra S. K. Datta J. K. Johri H. B. Singh A. Srivastava 《Journal of plant biochemistry and biotechnology.》2004,13(2):161-164
A protocol for large-scale propagation of Piper betle cvs Desawari and Desi Bangla was developed through axillary shoot proliferation. Due to systemic infection as well as high phenol content the crop was very difficult to establish in aseptic condition. But a mixture of 5 mg l?1 each of chloramphenicol and oxytetracyclin and 100 mg l?1 each of citric acid and ascorbic acid used in MS medium for 2 days helped in establishment. After 48 h, the explants were transferred to the antibiotic free medium having PVP and ascorbic acid (100 mg l?1 each), citric acid (50 mg l?1), and glutathione (20 mg l?1). Regular subculturing of the explants into liquid medium, use of antioxidants and incubation of the cultures in the dark for initial 7–10 days played a crucial role for keeping them fresh and green. Maximum numbers of axillary shoots were obtained with 2 mg l?1 BA and 0.2 mg l?1 NAA as growth supplements. The plants were rooted in 0.25 mg l?1 IBA and hardened in the soil. Phenolic compound analysis showed almost the same results in tissue-raised and in vivo grown plants in Desawari. 相似文献
110.
Studies using both Fisher 344 and Sprague-Dawley (SD) rat lines have shown that gestational and/or lactational maternal lead (Pb) exposure causes delayed reproductive maturation in their respective female offspring. Because these studies utilized different experimental regimens for dosing and for monitoring Pb levels, it has not been possible to determine which rat line provides the best model for low level Pb toxicity studies. This study was designed to address this issue. Adult Fisher and SD female rats were dosed with either a solution of PbAc containing 12 mg of Pb/ml or sodium acetate (NaAc) for controls. Dosing began 30 days prior to breeding and continued until their pups were weaned at 21 days of age. At the time of breeding and through weaning the blood lead (BPb) levels in the Fisher dams averaged 37.3 microg/dl and the SD dams averaged 29.9 microg/dl. Pb delayed the timing of puberty (p < 0.01) in Fisher offspring, and suppressed serum levels of luteinizing hormone (LH, p < 0.001) and estradiol (E2, p < 0.01). These effects did not occur in the SD offspring. Doubling the dose given to the SD rats increased their BPb levels to 62.6 microg/dl, yet there were still no effects noted. These results indicate that Fisher offspring are more sensitive to maternal Pb exposure with regard to puberty related insults than are SD rats, suggesting that the Fisher line may be a more reliable rodent model to study the effects of low level Pb toxicity. 相似文献