全文获取类型
收费全文 | 3663篇 |
免费 | 149篇 |
国内免费 | 9篇 |
专业分类
3821篇 |
出版年
2024年 | 4篇 |
2023年 | 38篇 |
2022年 | 107篇 |
2021年 | 178篇 |
2020年 | 131篇 |
2019年 | 136篇 |
2018年 | 141篇 |
2017年 | 128篇 |
2016年 | 166篇 |
2015年 | 225篇 |
2014年 | 250篇 |
2013年 | 279篇 |
2012年 | 294篇 |
2011年 | 278篇 |
2010年 | 155篇 |
2009年 | 142篇 |
2008年 | 176篇 |
2007年 | 154篇 |
2006年 | 136篇 |
2005年 | 133篇 |
2004年 | 110篇 |
2003年 | 77篇 |
2002年 | 82篇 |
2001年 | 27篇 |
2000年 | 20篇 |
1999年 | 19篇 |
1998年 | 7篇 |
1997年 | 11篇 |
1996年 | 11篇 |
1995年 | 10篇 |
1994年 | 15篇 |
1993年 | 8篇 |
1992年 | 16篇 |
1991年 | 10篇 |
1990年 | 14篇 |
1989年 | 10篇 |
1988年 | 9篇 |
1987年 | 4篇 |
1986年 | 7篇 |
1985年 | 8篇 |
1984年 | 5篇 |
1983年 | 5篇 |
1982年 | 11篇 |
1981年 | 7篇 |
1980年 | 7篇 |
1979年 | 8篇 |
1978年 | 12篇 |
1977年 | 10篇 |
1976年 | 8篇 |
1972年 | 4篇 |
排序方式: 共有3821条查询结果,搜索用时 0 毫秒
1.
2.
Although cryopreservation has been developed and optimized over the past decades, it causes various stresses, including cold shock, osmotic stress, and ice crystal formation, thereby reducing fertility. During cryopreservation, addition of cryoprotective agent (CPA) is crucial for protecting spermatozoa from freezing damage. However, the intrinsic toxicity and osmotic stress induced by CPA cause damage to spermatozoa. To identify the effects of CPA addition during cryopreservation, we assessed the motility (%), motion kinematics, capacitation status, and viability of epididymal spermatozoa using computer-assisted sperm analysis and Hoechst 33258/chlortetracycline fluorescence staining. Moreover, the effects of CPA addition were also demonstrated at the proteome level using two-dimensional electrophoresis. Our results demonstrated that CPA addition significantly reduced sperm motility (%), curvilinear velocity, viability (%), and non-capacitated spermatozoa, whereas straightness and acrosome-reacted spermatozoa increased significantly (p < 0.05). Ten proteins were differentially expressed (two decreased and eight increased) (>3 fold, p < 0.05) after CPA, whereas NADH dehydrogenase flavoprotein 2, f-actin-capping protein subunit beta, superoxide dismutase 2, and outer dense fiber protein 2 were associated with several important signaling pathways (p < 0.05). The present study provides a mechanistic basis for specific cryostresses and potential markers of CPA-induced stress. Therefore, these might provide information about the development of safe biomaterials for cryopreservation and basic ground for sperm cryopreservation. 相似文献
3.
4.
Beneficial effects of n-hexane bark extract of Onosma echioides L. on diabetic peripheral neuropathy
Ambreen Shoaib Badruddeen Rakesh Kumar Dixit Magdah Ganash George Barreto Ghulam Md Ashraf Hefazat Hussain Siddiqui 《Journal of cellular biochemistry》2019,120(10):16524-16532
Onosma echioides Linn (Boraginaceae) is the most frequently used curative herb widely used for kidney obstruction, sciatic pain, and gout. The present study was designed to investigate the therapeutic effects of n-hexane bark extract of O. echioides (OE) L. root in vivo against Streptozotocin-induced diabetic neuropathy in SD rats. For in vivo activity, the experiment was categorized into five different groups (n = 5). Group-I was considered as nondiabetic/normal control (NC) treated with 0.5% carboxymethyl cellulose (CMC), Group II as diabetic control, Group-III, IV, and V served as diabetic treated with OE 50, OE 100, and pregabalin at a dose of 50, 100, and 10 mg/kg body weight, orally, respectively. Body weight, blood glucose, oral glucose tolerance test, behavioral studies (motor coordination test, thermal hyperalgesia, cold allodynia, locomotor activity, oxidative biomarkers (thio barbituric acid reactive substances [TBARS], superoxide dismutase [SOD], glutathione [GSH], and catalase), and histopathology of the sciatic nerve were performed. Treatment with OE showed a dose-dependent increase in neuroprotective activity by improving the myelination and decreasing the axonal swelling of nerve fibers. The verdicts of behavioral activities showed a remarkable effect on animals after the treatment of extract and standard drug pregabalin. In conclusion, our findings supported the traditional application of OE and explored its importance in the management of diabetic neuropathy. Additional clinical experiments may provide novel therapeutic drugs for diabetes and its complications. 相似文献
5.
Demet Tademir Ayegül Karaküük‐yidoan Mustafa Ulali Tuba Takin‐Tok Emne Eln Oru‐Emre Hasan Bayram 《Chirality》2015,27(2):177-188
A series of new chiral thiosemicarbazones derived from homochiral amines in both enantiomeric forms were synthesized and evaluated for their in vitro antiproliferative activity against A549 (human alveolar adenocarcinoma), MCF‐7 (human breast adenocarcinoma), HeLa (human cervical adenocarcinoma), and HGC‐27 (human stomach carcinoma) cell lines. Some of compounds showed inhibitory activities on the growth of cancer cell lines. Especially, compound 17b exhibited the most potent activity (IC50 4.6 μM) against HGC‐27 as compared with the reference compound, sindaxel (IC50 10.3 μM), and could be used as a lead compound to search new chiral thiosemicarbazone derivatives as antiproliferative agents. Chirality 27:177–188, 2015. © 2014 Wiley Periodicals, Inc. 相似文献
6.
Autonomous DNA binding domains of lambda integrase recognize two different sequence families 总被引:35,自引:0,他引:35
The 40 kd lambda Integrase protein is shown to contain two autonomous DNA binding domains with different sequence specificities. Competition experiments in which the binding activity of Int is assayed through nuclease protection demonstrate the functional independence of the two DNA recognition specificities. Proteolytic cleavage of Int and footprinting analysis of the resulting two major peptides allow the physical separation and identification of two DNA binding domains: an amino-terminal peptide that interacts with "arm-type" sites and a carboxy-terminal peptide that binds to "core-type" sequences. In addition, the data suggest that the two domains can bind DNA simultaneously, consistent with a model in which Integrase would link two disparate DNA sequences. 相似文献
7.
Summary Snake flask experiments were carried out as a preliminary study of fat formation byTrichoderma
reesei (formallyviride) QM 9123 using a glucose based medium. The maximum quantity of fat production was 16% of the dry weight. The pH of the medium, as much as its composition, appeared to influence the quantity of fat that was produced. The fatty acids formed by the hydrolysis of the fats were found to be mainly unsaturated, with the 182 (linoleic) acid predominating. 相似文献
8.
Mini-exon derived RNA is a small nuclear RNA of trypanosomatid protozoa such asLeishmania which donates its 5′-terminal 39 nucleotides to the 5’-ends of cellular messenger RNAs by trans-splicing. We have cloned
a mini-exon derived RNA gene fromLeishmania donovani and studied its organization and expression. About 200 copies of the gene per haploid genome are organized as a tandem repeat
on a single chromosome. The gene is transcribed as a 95-nucleotide RNA. The first 39 nucleotides of mini-exon derived RNA
is also found at the 5′-terminus of a cellular mRNA (Β-tubulin), thus confirming its identity. Sequence analysis of the gene
and its flanking regions showed that while classical RNA polymerase II promoter elements such as TATA and CAAT are absent
from the 5′-upstream region, intragenic sequence motifs resembling RNA polymerase III promoter elements are present. The implications
of this finding for mini-exon derived RNA expression are discussed. 相似文献
9.
S. I. Hasan Barbara A. D. Blaney J. L. Turk 《Cancer immunology, immunotherapy : CII》1992,34(4):228-232
Summary This study investigates the effects of anticancer drugs and immunomodulating agents on the release of interleukin-6 (IL-6) from lipopolysaccharide-stimulated human peripheral blood mononuclear leucocytes in vitro. The addition of non-cytotoxic concentrations of Adriamycin (doxorubicin), vincristine and 4-OOH-cyclophosphamide (the in vitro active analogue of cyclophosphamide) resulted in suppression of IL-6 release. The drugs bleomycin, FK156 [d-lactoyl-l-alanyl--d-glutamyl-(l)-meso-diaminopimelyl-(l)-glycine], FK565 [heptanoyl--d-glutamyl-(l)-meso-diaminopimelyl-(d)-alanine] and the immunosuppressive agent cyclosporin A did not alter the release of IL-6 in the same experimental system. 相似文献
10.
A new saponin, leucasin, has been isolated from Leucas nutans and characterized on the basis of chemical investigation and spectroscopic studies as 3-O-[β-
-glucopyranosyl(1→2)β-
-glucopyranosyl]2,3β-dihydroxylup-20(29)-ene. Lupeol palmitate, sitosterol and stigmasterol were also isolated. 相似文献