全文获取类型
收费全文 | 2172篇 |
免费 | 150篇 |
专业分类
2322篇 |
出版年
2022年 | 27篇 |
2021年 | 53篇 |
2020年 | 26篇 |
2019年 | 33篇 |
2018年 | 43篇 |
2017年 | 37篇 |
2016年 | 76篇 |
2015年 | 87篇 |
2014年 | 102篇 |
2013年 | 132篇 |
2012年 | 142篇 |
2011年 | 137篇 |
2010年 | 86篇 |
2009年 | 74篇 |
2008年 | 96篇 |
2007年 | 91篇 |
2006年 | 97篇 |
2005年 | 78篇 |
2004年 | 67篇 |
2003年 | 48篇 |
2002年 | 44篇 |
2001年 | 59篇 |
2000年 | 44篇 |
1999年 | 44篇 |
1998年 | 18篇 |
1997年 | 20篇 |
1995年 | 15篇 |
1994年 | 15篇 |
1992年 | 26篇 |
1990年 | 29篇 |
1989年 | 17篇 |
1988年 | 25篇 |
1987年 | 20篇 |
1986年 | 30篇 |
1985年 | 21篇 |
1984年 | 20篇 |
1983年 | 18篇 |
1982年 | 20篇 |
1981年 | 25篇 |
1980年 | 13篇 |
1979年 | 24篇 |
1978年 | 14篇 |
1977年 | 15篇 |
1975年 | 19篇 |
1974年 | 17篇 |
1973年 | 17篇 |
1972年 | 22篇 |
1971年 | 13篇 |
1970年 | 15篇 |
1969年 | 14篇 |
排序方式: 共有2322条查询结果,搜索用时 0 毫秒
161.
In bacteria, biogenesis of cell wall at the division site requires penicillin-binding protein 3 (PBP3) (or Ftsl). Using pull-down, bacterial two-hybrid, and peptide-based interaction assays, we provide evidence that FtsW of Mycobacterium tuberculosis (FtsWMTB) interacts with PBP3 through two extracytoplasmic loops. Pro306 in the larger loop and Pro386 in the smaller loop of FtsW are crucial for these interactions. Fluorescence microscopy shows that conditional silencing of ftsW in Mycobacterium smegmatis prevents cell septation and positioning of PBP3 at mid-cell. Pull-down assays and conditional depletion of FtsW in M. smegmatis provide evidence that FtsZ, FtsW and PBP3 of mycobacteria are capable of forming a ternary complex, with FtsW acting as a bridging molecule. Bacterial three-hybrid analysis suggests that in M. tuberculosis, the interaction (unique to mycobacteria) of FtsZ with the cytosolic C-tail of FtsW strengthens the interaction of FtsW with PBP3. ftsW of M. smegmatis could be replaced by ftsW of M. tuberculosis. FtsWMTB could support formation of the FtsZ-FtsW-PBP3 ternary complex in M. smegmatis. Our findings raise the possibility that in the genus Mycobacterium binding of FtsZ to the C-tail of FtsW may modulate its interactions with PBP3, thereby potentially regulating septal peptidoglycan biogenesis. 相似文献
162.
Relative thermotolerance of the enzyme, L-myo-inositol-1-phosphate synthase (MIPS; EC: 5.5.1.4), from the chloroplastic and cytosolic sources of Diplopterygium glaucum was studied. The purification involved streptomycin sulphate precipitation, ammonium sulphate fractionation, ion-exchange chromatography, and molecular sieve chromatography. After the final chromatography, 16.62% of chloroplastic and 13.47% of cytosolic MIPS could be recovered. Between 15 degrees C and 55 degrees C, the two forms of MIPS exhibited differential thermal stability, which is related to the presence of the MIPS co-factor, NAD+. Added NAD+ increased the lower thermotolerance of the chloroplastic MIPS and the removal of 'built-in' NAD+ decreased the higher thermal stability of the cytosolic MIPS. 相似文献
163.
Ya. V. Makarova I. V. Shelukhina A. K. Mukherjee D. V. Kuznetsov V. I. Tsetlin Yu. N. Utkin 《Doklady. Biochemistry and biophysics》2017,475(1):253-255
Fluorescent derivatives are widely used to study the structure and functions of proteins. Quantum dots (QDs), fluorescent semiconductor nanocrystals, have a high quantum yield and are much more resistant to bleaching compared to organic dyes. Conjugates of α-neurotoxins with QDs were used for visualization of human α7 acetylcholine receptors heterologously expressed in GH4C1 pituitary adenoma cells. Specific staining of cells by the conjugated toxins was observed. 相似文献
164.
Length–weight and length–length relationship of Strongylura strongylura (van Hasselt, 1823) and Hyporhamphus limbatus (Valenciennes, 1847) from Chilika Lake,India 下载免费PDF全文
S. K. Karna M. Mukherjee V. R. Suresh R. K. Manna H. M. Manas R. K. Raman 《Zeitschrift fur angewandte Ichthyologie》2017,33(3):640-641
Analyzed were the length–weight relationship (LWR) and length–length relationship (LLR) of two fish species, Strongylura strongylura (family Belonidae) and Hyporhamphus limbatus (family Hemiramphidae) from Chilika Lake, India. A total of 616 specimens were sampled bi‐monthly from August 2014 to June 2016 using seine nets and screen barrier nets operated by local fishermen that were used for the present estimates. 相似文献
165.
Irom?Harimala?Chanu Laishram?Ronibala?Devi Nonibala?Khumanthem N.?Irabanta?Singh Dalip?Kumar Okram?Mukherjee?SinghEmail author 《Russian Journal of Bioorganic Chemistry》2017,43(2):177-185
Knoevenagel cyclocondensations of α-hydroxy naphthaldehyde with β-oxodithioesters and ketene dithioacetals yielded 2H-benzo[f]chromene-2-thiones and 2H-benzo[f]chromen-2-ones, respectively, in high yields. The newly synthesized compounds were evaluated for antifungal and antibacterial activities. Among them, compounds (2-furyl)(3-thioxo-3H-benzo[f]chromen-2-yl)methanone and phenyl(3-oxo-3H-benzo[f]chromen-2-yl)methanone exhibited excellent antifungal activity against tested fungi Curvularia lunata and Fusarium moniliforme. The highest antibacterial activity against the tested bacteria Escherichia coli and Staphylococcus aureus was observed for (4-chlorophenyl)(3-oxo-3H-benzo[f]chromen-2-yl)methanone. The results of antimicrobial screening demonstrate that (2-furyl)(3-thioxo-3H-benzo[f]chromen-2-yl)methanone, phenyl(3-oxo-3H-benzo[f]chromen-2-yl)methanone, and (4-chlorophenyl)(3-oxo-3H-benzo[f]chromen-2-yl)methanone are promising as antimicrobial drugs. 相似文献
166.
Gold nanoparticles–conjugated quercetin induces apoptosis via inhibition of EGFR/PI3K/Akt–mediated pathway in breast cancer cell lines (MCF‐7 and MDA‐MB‐231) 下载免费PDF全文
Solaimuthu Balakrishnan Sudip Mukherjee Sourav Das Firdous Ahmad Bhat Paulraj Raja Singh Chitta Ranjan Patra Jagadeesan Arunakaran 《Cell biochemistry and function》2017,35(4):217-231
Epidermal growth factor plays a major role in breast cancer cell proliferation, survival, and metastasis. Quercetin, a bioactive flavonoid, is shown to exhibit anticarcinogenic effects against various cancers including breast cancer. Hence, the present study was designed to evaluate the effects of gold nanoparticles–conjugated quercetin (AuNPs‐Qu‐5) in MCF‐7 and MDA‐MB‐231 breast cancer cell lines. Borohydride reduced AuNPs were synthesized and conjugated with quercetin to yield AuNPs‐Qu‐5. Both were thoroughly characterized by several physicochemical techniques, and their cytotoxic effects were assessed by MTT assay. Apoptotic studies such as DAPI, AO/EtBr dual staining, and annexin V‐FITC staining were performed. AuNPs and AuNPs‐Qu‐5 were spherical with crystalline nature, and the size of particles range from 3.0 to 4.5 nm. AuNPs‐Qu‐5 exhibited lower IC50 value compared to free Qu. There was a considerable increase in apoptotic population with increased nuclear condensation seen upon treatment with AuNPs‐Qu‐5. To delineate the molecular mechanism behind its apoptotic role, we analysed the proteins involved in apoptosis and epidermal growth factor receptor (EGFR)–mediated PI3K/Akt/GSK‐3β signalling by immunoblotting and immunocytochemistry. The pro‐apoptotic proteins (Bax, Caspase‐3) were found to be up regulated and anti‐apoptotic protein (Bcl‐2) was down regulated on treatment with AuNPs‐Qu‐5. Additionally, AuNPs‐Qu‐5 treatment inhibited the EGFR and its downstream signalling molecules PI3K/Akt/mTOR/GSK‐3β. In conclusion, administration of AuNPs‐Qu‐5 in breast cancer cell lines curtails cell proliferation through induction of apoptosis and also suppresses EGFR signalling. AuNPs‐Qu‐5 is more potent than free quercetin in causing cancer cell death, and hence, this could be a potential drug delivery system in breast cancer therapy. 相似文献
167.
168.
Reactivity switching and selective activation of C-1 or C-3 in 2,3-unsaturated thioglycosides, namely, 2,3-dideoxy-1-thio-d-hex-2-enopyranosides are reported. The reactivity switching allowed activation of either C-1 or C-3, with the use of either N-iodosuccinimide (NIS)/triflic acid (TfOH) or TfOH alone. C-1 glycosylation with alcohol acceptors occurred in the presence of NIS/TfOH, without the acceptors reacting at C-3. On the other hand, reaction of 2,3-unsaturated thioglycosides with alcohols mediated by triflic acid led to transposition of C-1 ethylthio-moiety to C-3 intramolecularly, to form 3-ethylthio-glycals. Resulting glycals underwent glycosylation with alcohols to afford 3-ethylthio-2-deoxy glycosides. However, when thiol was used as an acceptor, only a stereoselective addition at C-3 resulted, so as to form C-1, C-3 dithio-substituted 2-deoxypyranosides. 相似文献
169.
170.
A case of translocation heterozygosity has been discovered in gardenCanna. Morphologically the heterozygote is distinctive, being a pygmy type with small flowers which do not open. Cytologically it shows a ring or a chain of 4 plus 7 bivalents. The present observations reveal that rings disjunct usually in adjacent, and chains in an alternate manner. The subsequent course of meiosis is normal. The variety is totally sterile both after self and cross pollination. It has very likely arisen as a hybrid between two parents differing in one interchange. 相似文献