全文获取类型
收费全文 | 40759篇 |
免费 | 2621篇 |
国内免费 | 14篇 |
出版年
2021年 | 524篇 |
2020年 | 352篇 |
2019年 | 481篇 |
2018年 | 739篇 |
2017年 | 737篇 |
2016年 | 1088篇 |
2015年 | 1585篇 |
2014年 | 1801篇 |
2013年 | 2290篇 |
2012年 | 2622篇 |
2011年 | 2594篇 |
2010年 | 1644篇 |
2009年 | 1428篇 |
2008年 | 1951篇 |
2007年 | 1914篇 |
2006年 | 1898篇 |
2005年 | 1852篇 |
2004年 | 1663篇 |
2003年 | 1541篇 |
2002年 | 1537篇 |
2001年 | 688篇 |
2000年 | 599篇 |
1999年 | 561篇 |
1998年 | 407篇 |
1997年 | 281篇 |
1996年 | 298篇 |
1995年 | 269篇 |
1994年 | 272篇 |
1993年 | 269篇 |
1992年 | 489篇 |
1991年 | 447篇 |
1990年 | 342篇 |
1989年 | 432篇 |
1988年 | 432篇 |
1987年 | 391篇 |
1986年 | 359篇 |
1985年 | 415篇 |
1984年 | 385篇 |
1983年 | 320篇 |
1982年 | 249篇 |
1979年 | 353篇 |
1978年 | 264篇 |
1975年 | 245篇 |
1974年 | 371篇 |
1973年 | 353篇 |
1972年 | 311篇 |
1971年 | 307篇 |
1970年 | 304篇 |
1969年 | 292篇 |
1968年 | 237篇 |
排序方式: 共有10000条查询结果,搜索用时 296 毫秒
151.
Marta Munzarová Daniela Zemanová Jan Kovařík Zdeněk Pačovský Aleš Rejthar Jiří Bártek 《Cancer immunology, immunotherapy : CII》1987,24(3):272-274
Summary Skin tests with autologous cholesteryl hemisuccinate (CHS)-treated and untreated cells were performed in ten metastatic melanoma patients. In the majority of cases evident reaction was noted with CHS-treated cells (9/10) while the reaction with untreated cells was mostly negative (7/10). Tumour cell suspensions used for skin tests were characterized for reactivity with monoclonal antibody TAL 1B5 detecting the HLA-DR alpha chain. There were no differences between CHS-treated and untreated cells with respect to HLA-DR expression and no correlation was found between grade of skin reaction to CHS-treated cells and the proportion of HLA-DR positive cells in the injected cell sample. 相似文献
152.
Michael G?ttfert Joseph W. Lamb Regula Gasser Jan Semenza Hauke Hennecke 《Molecular & general genetics : MGG》1989,215(3):407-415
Summary By insertional and deletional marker replacement mutagenesis the common nod region of Bradyrhizobium japonicum was examined for the presence of additional, essential nodulation genes. An open reading frame located in the 800 bp large intergenic region between nodD1 and nodA did not appear to be essential for nodulation of soybean. Furthermore, a strain with a deletion of the nodI- and nodJ-like genes downstream of nodC had a Nod+ phenotype. A mutant with a 1.7 kb deletion immediately downstream of nodD1 considerably delayed the onset of nodulation. This region carried a second copy of nodD (nodD2). A nodD1-nodD2 double mutant had a similar phenotype to the nodD2 mutant. Using a 22-mer oligonucleotide probe partially identical to the nod box sequence, a total of six hybridizing regions were identified in B. japonicum genomic DNA and isolated from a cosmid library. Sequencing of the hybridizing regions revealed that at least three of them represented true nod box sequences whereas the others showed considerable deviations from the consensus sequence. One of the three nod box sequences was the one known to be associated with nodA, whereas the other two were located 60 to 70 kb away from nif cluster I. A deletion of one of these two sequences plus adjacent DNA material mmutant 308) led to a reduced nodulation on Vigna radiata but not on soybean. Thus, this region is probably involved in the determination of host specificity.Dedicated to Prof. Giorgio Semenza on the occasion of his 60th birthday 相似文献
153.
John Stanley Jan van Slooten David N. Dowling Turlough Finan William J. Broughton 《Molecular & general genetics : MGG》1989,217(2-3):528-532
Summary The clonedntrA (rpoN) gene andntrA mutants ofRhizobium meliloti were used to isolate the homologous gene from the broad-host rangeRhizobium sp. NGR234 by hybridization and interspecies complementation. The NGR234 locus was analyzed by deletion and insertional mutagenesis.
A site-directedntrA mutant, NGR234rn1, was made with an interposon, GmI, and its phenotype was examined ex planta and in symbiosis. NGR234rn1 formed Fix− nodules on six genera tested from among its legume hosts, including both indeterminate and determinate nodule-type plants.
Formation of nodules onMacroptilium was delayed, and expression of anR. meliloti nodABC-lacZ fusion was reduced by the mutant allele. 相似文献
154.
Summary The Bacillus subtilis cdd gene encoding cytidine/2-deoxycytidine deaminase has been located by transduction at approximately 225 degrees on the chromosome, and the gene order rpC-lys-cdd-aroD was established. The gene was isolated from a library of B. subtilis DNA cloned in D69 by complementation of an Escherichia coli cdd mutation. Minicell experiments revealed a molecular mass of 14000 dalton for the cytidine deaminase subunit encoded by the cloned DNA fragment. The molecular weight of the native enzyme was determined to be 58000, suggesting that it consists of four identical subunits. The nucleotide sequence of 1170 bp, including the cdd gene, was determined. An open reading frame encoding a polypeptide with a calculated molecular mass of 14800 dalton was deduced to be the coding region for cdd. The deduced amino acid composition of the 136-amino acid-long subunit shows that it contains six cysteine residues. A computer search in the GenBank DNA sequence library revealed that the 476 bp HindIII fragment containing the putative promoter region and the first ten codons of cdd is identical to the P43 promoter-containing fragment previously isolated by Wang and Doi (1984). They showed that the fragment contained overlapping promoters transcribed by B. subtilis 43 and 37 RNA polymerase holoenzymes during growth and stationary phase.Abbreviations SDS
sodium dodecyl sulphate
- Ap
ampicillin resistance
- Tetr
tetracycline resistance
- Kmr
kanamycin resistance 相似文献
155.
Dirk Bosch Monica Scholten Cora Verhagen Jan Tommassen 《Molecular & general genetics : MGG》1989,216(1):144-148
Summary PhoE protein of Escherichia coli K12 is an outer membrane protein which is supposed to span the membrane sixteen times. By creating a deletion which removes the last membrane-spanning fragment and studying the localization of the truncated PhoE, we show that this fragment is indispensable for trimerization and outer membrane localization. In addition, circumstantial evidence for the proposed topology model of the protein was obtained. An insertion mutation in a region supposed to be cell surface-exposed, interferes with the binding of a monoclonal antibody which recognizes a cell surface-exposed epitope of the protein. 相似文献
156.
M Marczyńska 《Polski tygodnik lekarski (Warsaw, Poland : 1960)》1989,44(28-29):677-678
The first case of Q fever in Poland in a 5-year girl is presented. A girl is inhabitant of the Lublin region where this disease is of endemic character. Q fever was diagnosed on the base of the clinical examinations and serological tests. The course of the disease was acute. Doxycycline and lincomycin were given. A short time lapse between the treatment and eradication of Coxiella burnetii antigen indicates rather spontaneous recovery. 相似文献
157.
Psychological sequelae of abdominal stoma and the value of informing the patients and their families
J Fryc-Martyńska 《Polski tygodnik lekarski (Warsaw, Poland : 1960)》1989,44(20):469-471
Results of investigations carried out in a 500-person group of patients with stoma and their practical applications are discussed. 1. Despite operational shock, the majority of patients is able to adopt to the new situation and develop different life-style. 2. Rehabilitation facilities pre-operational management and provides an information on stoma before surgery. Postoperative management should consider psychosocial aspects of the stoma. 3. An important role in rehabilitation process play: preparation of the patients' families before the surgery including information on the diagnosis, prognosis and planned therapy. 4. Persons who underwent the same surgery and continue active life may favourably contribute to the postoperational care of patients with stoma. Activity of so-called patients clubs plays also positive role. 相似文献
158.
J Chodakowska B Wocial H Ignatowska-Switalska K Knypl E Brym E Czerniewska J Wac?awek-Maczkowska E Jab?ońska-Skwiecińska D Drygieniec W Januszewicz 《Polski tygodnik lekarski (Warsaw, Poland : 1960)》1989,44(12-13):297-300
An effect of enalapril maleate on the activity of renin-angiotensin-aldosterone system and sympathetic reactivity, erythrocyte prostaglandin and sodium levels as well as blood beta-endorphin was investigated in 28 patients with the essential arterial blood hypertension. It was found that enalapril maleate significantly increased plasma renin activity, decreased plasma norepinephrine and its 24-hour excretion, and decreased erythrocyte beta-endorphin and sodium levels. Blood epinephrine and aldosterone levels and their daily excretion remained unchanged similarly to prostaglandins. The above results suggest that a decrease in sympathetic system activity and intracellular sodium concentration may play a role in the hypotensive action of enalapril maleate related to the inhibition of angiotensin II formation. 相似文献
159.
M Koehler H Buba?a D Sońta-Jakimczyk E Guzikowska A Janik-Moszant M Wieczorek J Ho?owiecki 《Polski tygodnik lekarski (Warsaw, Poland : 1960)》1989,44(40-42):879-81, 884
Blasts phenotype was determined in 61 children with the acute lymphoblastic leukemia. Non-T-cell acute lymphoblastic leukemia was diagnosed in 51 children. Stages of blasts differentiation were determined with the aid of monoclonal antibodies set using alkaline phosphatase-anti-alkaline phosphatase technique. Blasts in 50 patients belonged to B subpopulation confirmed by the presence of panB CD19 and CD22 antigens. Common antigen was seen in 76.5% of the examined patients with non-T-cell acute lymphoblastic leukemia. Cases of non-T-cell acute lymphoblastic leukemia were divided into 8 subgroups depending on the antigens of B-cells differentiation. An identification of pre-B subgroups of the acute lymphoblastic leukemia indicates heterogenicity of the acute lymphoblastic leukemias in childhood and enables their classification into groups corresponding to the early stages of lymphoblasts maturation. 相似文献
160.