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排序方式: 共有1177条查询结果,搜索用时 46 毫秒
51.
We studied in the seedlings of two rice cultivars (Malviya-36 and Pant-12) the effect of increasing levels of arsenic in situ on the content of sugars and the activity of several enzymes of starch and sucrose metabolism: alpha-amylase (EC 3.2.1.1), beta-amylase (EC 3.2.1.2), starch phosphorylase (EC 2.4.1.1), acid invertase (EC 3.2.1.26), sucrose synthase (EC 2.4.1.13) and sucrose phosphate synthase (EC 2.4.1.14). During a growth period of 10-20 d As2O3 at 25 and 50 microM in the growth medium caused an increase in reducing, non-reducing and total soluble sugars. An increased conversion of non-reducing to reducing sugars was observed concomitant with As toxicity. The activities of alpha-amylase, beta-amylase and sucrose phosphate synthase declined, whereas starch phosphorylase, acid invertase and sucrose synthase were found to be elevated. Results indicate that in rice seedlings arsenic toxicity causes perturbations in carbohydrate metabolism leading to the accumulation of soluble sugars by altering enzyme activity. Sucrose synthase possibly plays a positive role in synthesis of sucrose under As-toxicity. 相似文献
52.
53.
Inactivation of Cyanobacterial Nitrogenase After Exposure to Ultraviolet-B Radiation 总被引:2,自引:0,他引:2
Exposure of the N2-fixing cyanobacterium Anabaena BT2 to ultraviolet-B radiation (2.5 W m−2) for 30 min resulted in complete loss of nitrogenase activity but 100% cell killing occurred only after a 90-min exposure.
Inactivation of nitrogenase activity was not specific to Anabaena BT2; other species also showed a similar effect. The time required for 100% killing and inactivation of nitrogenase activity
differed in various species, and this difference may be ascribed to the presence of different levels of UV-B protection mechanisms
in individual species. Inhibition of nitrogenase activity was immediate, since exposure of cultures to UV-B for as little
as 5 min elicited some inhibition of activity. The activity of UV-B-inhibited nitrogenase did not recover upon transfer of
exposed cells to fluorescent light, suggesting that the inhibition may be due to specific inactivation of the enzyme. By employment
of inhibitors of protein synthesis and PS-II activity, it was demonstrated that restoration of nitrogenase activity in a UV-B-treated
culture occurred by fresh synthesis of nitrogenase polypeptide. Our findings suggest that estimation of nitrogenase activity
in diazotrophic species may be used as a marker enzyme for assessing the impact of UV-B radiation.
Received: 13 June 2002 / Accepted: 22 July 2002 相似文献
54.
Debnath B Gayen S Bhattacharya S Samanta S Jha T 《Bioorganic & medicinal chemistry》2003,11(24):5493-5499
Pyridoacridine ascididemin analogues have been reported as anticancer agents for their interesting antitumor activity against human cancer cells. A quantitative structure–activity relationship (QSAR) analysis of ascididemin analogues was attempted using the physicochemical parameters and the electrotopological state atom (ETSA) indices. This study indicates that the electron withdrawing substituents with higher MR (molar refractivity) value at R1 position favor the anti-tumor activity and the presence of NHR (R is hydrogen or alkyl group) at the R3 position has contribution to the anti-tumor activity. ETSA indices have been incorporated as independent variable in the QSAR model with physicochemical parameters. It clearly suggests the importance of atoms 2, 3, 4, 5, 6 and 7 to the anti-tumor activity. 相似文献
55.
Prolonged exposure to progesterone prevents induction of protective mucosal responses following intravaginal immunization with attenuated herpes simplex virus type 2 总被引:1,自引:0,他引:1 下载免费PDF全文
Depo-Provera (Depo) is a long-acting progestational formulation that is a popular form of contraception for women. In animal models of sexually transmitted diseases, it is used to facilitate infection. Here we report that treatment with Depo, in a mouse model of genital herpes simplex virus type 2 (HSV-2), altered immune responses depending on the length of time that animals were exposed to Depo prior to immunization. Mice immunized intravaginally (i.vag.) with an attenuated strain (TK(-)) of HSV-2 following longer (15 days) exposure to Depo (Depo 15 group) failed to show protection when challenged with wild-type HSV-2. In contrast, mice that were immunized shortly after Depo treatment (5 days; Depo 5 group) were fully protected and showed no genital pathology after HSV-2 challenge. High viral titers were detected in the vaginal washes of the Depo 15 group up to 6 days postchallenge. In contrast, no viral shedding was observed beyond day 3 postchallenge in the Depo 5 group. Following i.vag. TK(-) immunization, high levels of gamma interferon (IFN-gamma) were detected locally in vaginal washes of the Depo 5 group but not the Depo 15 group. After HSV-2 challenge, an early peak of IFN-gamma in the Depo 5 group coincided with clearance of the virus. In Depo 15 animals IFN-gamma was present throughout the 6 days postinfection. HSV-2-specific T-cell cytokine responses measured in the lymph node cells of Depo 5 TK(-)-immunized mice indicated a significantly higher Th1 response than that of Depo 15 TK(-)-immunized mice. The protection after HSV-2 challenge in the Depo 5 group correlated with increased local HSV-2 glycoprotein B (gB)-specific immunoglobulin G (IgG) and IgA responses seen in the vaginal secretions. The Depo 15 group had poor gB-specific antibody responses in the genital tract after HSV-2 challenge. These results indicate that longer exposure to Depo leads to poor innate and adaptive immune responses to HSV-2 that fail to protect mice from subsequent genital challenges. 相似文献
56.
Covalent modification of cysteine 193 impairs ATPase function of nucleotide-binding domain of a Candida drug efflux pump 总被引:3,自引:0,他引:3
Jha S Karnani N Lynn AM Prasad R 《Biochemical and biophysical research communications》2003,310(3):869-875
N-ethylmaleimide (NEM) impairs the ATPase function of N-terminal NBD of Candida drug resistance gene product Cdr1p. To identify the reactive cysteine(s) for such a contribution, we adopted a three-arm approach that included covalent modification, cysteine mutagenesis, and structure homology modeling. The covalent modification results clearly indicate the ability of NEM and iodoacetic acid (IAA) to potently inhibit the ATPase activity of N-terminal NBD. Since this domain contains five cysteine residues in its sequence, we mutated each and found four of these (C325A, C363A, C402A, and C462A) to stay sensitive to NEM/IAA modification and influence ATPase activity, while C193A mutation completely abrogated the catalytic function. The structural homology modeling data further validate these biochemical findings by ruling out any plausible interactions within the cysteine residues, and deriving the importance of Cys-193 in lying at a bond length clearly feasible to interact with ATP and divalent cation to critically influence ATP hydrolysis. 相似文献
57.
Two plant alkaloids isolated from<Emphasis Type="Italic">Corydalis longipes</Emphasis> as potential antifungal agents 总被引:1,自引:0,他引:1
The alkaloids N-methylhydrasteine hydroxylactam and 1-methoxyberberine chloride were isolated from Corydalis longipes. Both alkaloids showed high efficacy individually (in concentration of 50-150 ppm) and also in a 1:1 mixture against spore germination of some fungi, viz. Alternaria alternata, A. brassicae, Curvularia maculans, Curvularia sp., Colletotrichum gloeosporioides, Colletotrichum sp., Helminthosporium speciferum, H. pennisetti, Helminthosporium sp., and Ustilago cynodontis. The antifungal effect of single compounds was dose-dependent. If the mutual ratio of the two components in the mixture was changed from 1:1 to a major content of any of the two compounds, the inhibitory effect on spore germination decreased. 相似文献
58.
59.
Endostatin is a potential inhibitor of Wnt signaling 总被引:33,自引:0,他引:33
Hanai J Gloy J Karumanchi SA Kale S Tang J Hu G Chan B Ramchandran R Jha V Sukhatme VP Sokol S 《The Journal of cell biology》2002,158(3):529-539
60.
Dimmock JR Jha A Zello GA Sharma RK Shrivastav A Selvakumar P Allen TM Santos CL Balzarini J De Clercq E Manavathu EK Stables JP 《Journal of enzyme inhibition and medicinal chemistry》2003,18(4):325-332
A series of novel 3,5-bis(phenylmethylene)-1-(N-arylmaleamoyl)-4-piperidones 3 have been synthesized which displayed potent cytotoxicity towards human Molt 4/C8 and CEM T-lymphocytes as well as murine P388 and L1210 leukemic cells. In contrast, the related N-arylmaleamic acids 4 possessed little or no cytotoxicity in these four screens. Molecular modeling revealed certain interplanar and bond angles and interatomic distances which were perceived to contribute to the observed bioactivity as well as providing suggestions for future structural modifications of the piperidones 3. Evaluation of representative compounds in series 3 and 4 on the activity of human N-myristoyltransferase revealed that, at the maximum concentration utilized, namely 250 microM, only weak inhibiting properties were displayed by some of the compounds in series 4. Various members of series 3 and 4 were well tolerated in mice. 相似文献