全文获取类型
收费全文 | 11654篇 |
免费 | 446篇 |
国内免费 | 839篇 |
出版年
2024年 | 19篇 |
2023年 | 89篇 |
2022年 | 141篇 |
2021年 | 175篇 |
2020年 | 157篇 |
2019年 | 236篇 |
2018年 | 214篇 |
2017年 | 185篇 |
2016年 | 186篇 |
2015年 | 287篇 |
2014年 | 391篇 |
2013年 | 575篇 |
2012年 | 371篇 |
2011年 | 474篇 |
2010年 | 332篇 |
2009年 | 479篇 |
2008年 | 552篇 |
2007年 | 593篇 |
2006年 | 676篇 |
2005年 | 565篇 |
2004年 | 491篇 |
2003年 | 483篇 |
2002年 | 408篇 |
2001年 | 396篇 |
2000年 | 383篇 |
1999年 | 342篇 |
1998年 | 384篇 |
1997年 | 292篇 |
1996年 | 263篇 |
1995年 | 263篇 |
1994年 | 259篇 |
1993年 | 289篇 |
1992年 | 229篇 |
1991年 | 202篇 |
1990年 | 222篇 |
1989年 | 170篇 |
1988年 | 140篇 |
1987年 | 125篇 |
1986年 | 114篇 |
1985年 | 161篇 |
1984年 | 154篇 |
1983年 | 61篇 |
1982年 | 90篇 |
1981年 | 63篇 |
1980年 | 61篇 |
1979年 | 38篇 |
1978年 | 26篇 |
1977年 | 29篇 |
1976年 | 22篇 |
1973年 | 20篇 |
排序方式: 共有10000条查询结果,搜索用时 156 毫秒
151.
The neurointermediary lobes from 190 rat pituitaries were homogenized in an acidic medium which inhibits peptidase activity and maximizes the solubilization of undamaged peptides. Octadecylsilyl-silica (ODS-silica) was used to extract the supernatant of the tissue homogenate. The ODS-silica eluate, now largely protein and salt free, was subjected to reversed-phase high-performance liquid chromatography (HPLC) employing 0.1% trifluoroacetic as counter ion. The column eluates were monitored for beta-endorphin immunoreactivity. Five immunoreactive components were observed. The most hydrophobic of these was repurified on the same HPLC column using 0.13% heptafluorobutyric acid as counter ion. Characterization of the purified peptide by gel permeation HPLC, amino acid analysis, and tryptic fragmentation indicated that it corresponded in structure to alpha-N-acetyl-beta-endorphin1-26. Amino acid analysis of the native peptide and its trypsin and carboxypeptidase fragments indicated that an alanyl residue occupies position 26. This finding is in contrast to the sequence predicted for the beta-lipotropin/corticotropin precursor by recombinant DNA techniques which suggests that the 26th residue of the beta-endorphin molecule should be valine. 相似文献
152.
Summary The response of the cotton plant (Gossypium hirsutum L.) to 9.0 and 12.5 cm intra- and 75.0 and 96.5 cm inter-row spacing was studied under irrigation with saline water (5.5 dS/m, SAR 18). In general, the dry weight per plant matter, the leaf area, number of bolls and flowers, and yield per plant were all affected significantly by intra-row spacing but, not by inter-row spacing. However, on a unit area basis, they were affected only by the inter-row spacing. This indicates that competition between plants exists when intra-row spacing is reduced, whereas no significant competition occurs due to a decrease in the inter-row spacing. Although the effect of intra-row spacing on yield for a unit area was found to be not significant, the effect of inter-row spacing was significant. Yield in plots with the conventional spacing (96.5 cm between rows and 12.5 cm between plants in the row) was 4863 kg/ha, whereas the yield in plots with 75 cm between rows was about 23% higher (5974 kg/ha). The lint percentage and the plant height were not affected significantly by either intra- or inter-row spacings.Contribution from the Institute of Soils and Water, Agricultural Research Organization, The Volcani Center, Bet Dagan 50250, Israel. No.676-E, 1983 series. 相似文献
153.
Cyanophora paradoxa Korshikov synchronized autotrophically in a light-dark regime of 14 h light and 10 h dark divides in the last two hours of the dark period. The division rate of the free-living blue-green alga, Synechococcus leopoliensis Raciborski, at identical culture conditions (24°C; 32 W m−2 ) is only slightly lowered in the light period. The comparison of thylakoid differentiation in the endocyanelles of Cyanophora paradoxa and in Synechococcus leopoliensis during the light-dark regime yields (1) the same ensemble of pigment-protein complexes in both organisms, (2) comparable syntheses of chlorophyll and phycobilins of Cyanophora paradoxa grown under 32 W m−2 and of Synechococcus leopoliensis grown under light intensities below 9.2 W m−2 , and (3) identical photosynthetic oxygen evolution during the light period of the light-dark regime with minima at the beginning, in the middle (6th–7th h), and at the end of the light period. In both organisms this stage-specific oxygen evolution is inhibited by treatment with chloroamphenicol. Cycloheximide, however, causes no significant alterations. Results are discussed in view of the endosymbiotic theory. 相似文献
154.
Isolation,purification and chemical composition of maize root cap slime 总被引:10,自引:0,他引:10
Annie Chaboud 《Plant and Soil》1983,73(3):395-402
Summary The total root exudate isolated axenically from roots is shown to constitute an extremely heterogenous population of particulate and soluble material. Differences in protein and total sugars contents, and neutral sugar composition throughout stages of total root exudate purification are reported. The importance of controlled collection and purification conditions to ensure valid analysis and composition of purified maize root cap slime are discussed. 相似文献
155.
de Vries J. N. 《TAG. Theoretical and applied genetics. Theoretische und angewandte Genetik》1983,66(3-4):329-339
Summary The recombination fraction between the interstitially located gene an and interchange 303 of rye was found to be 0.244±0.038 in a test cross using the translocation as the male parent. In first metaphase translocation configurations in pollen mother cells of the same plant, the chiasma frequency between an and the translocation breakpoint was found to be significantly more than twice the recombination fraction. Recombination was concluded to be masked by a difference in the alternate frequency between configurations without interstitial chiasmata and configurations with interstitial chiasmata, the effect of the first type being of major importance. Random centromere orientation of translocation multivalents with interstitial chiasmata was concluded to be a realistic assumption. The exceptionally high recombination between an and translocation 303 is discussed. Consideration is also given to the use of interchanges in the establishment of a marker's chromosomal position, and to the use of translocation chromosomes in balanced systems for hybrid breeding purposes. 相似文献
156.
Genetics of osteal plate polymorphism and microevolution of threespine stickleback (Gasterosteus aculeatus L.) 总被引:1,自引:0,他引:1
V. V. Ziuganov 《TAG. Theoretical and applied genetics. Theoretische und angewandte Genetik》1983,65(3):239-246
Summary The results of genetical studies of osteal plate polymorphism of threespine stickleback Gasterosteus
aculeatus reported to date (Munzing 1959; Hagen and Gilbertson 1973; Avise 1976) are discussed and proposed inheritance models are considered. Results of crosses between the morphs of G. aculeatus from the White Sea are presented. An attempt has been made by the author to devise a unifying model for the inheritance of plate morphs within the whole range of G. aculeatus. The role of polymorphism in the microevolutionary processes taking place within this complex species is discussed. 相似文献
157.
Behavior of lactating rats in a dual-chambered maternity cage 总被引:2,自引:0,他引:2
Videotape sampling of behavior in a dual-chambered apparatus indicates that the continuous monitoring of the amount of time a mother spends in the cage with its litter can be taken as a valid reflection of maternal behavior. Nursing is the principal behavior of lactating females while in the compartment with their litters; lying still, consummatory behavior, and activity occur with greater frequency in the cage away from the litter. Both the time that mothers spend with their litters and nursing behavior displayed a 24-hr rhythm with crest values occurring during the period of light. 相似文献
158.
Laurent Bonneau Nicole Beranger-Novat Jeannine Monin Josette Martin-Tanguy 《Plant Growth Regulation》1967,16(1):5-10
In vitro formation of roots and somatic embryos is obtained from cotyledon explants of a Spindle tree (Euonymus europaeus L.) cultured on two different media: a medium inducing callus formation and the production of roots, and a medium inducing callus formation, root and somatic embryo production. We studied the effects of -difluoromethylornithine (DFMO), a specific, irreversible inhibitor of ornithine decarboxylase (ODC) on root and somatic embryo production, growth and titers of putrescine in Euonymus explants and explant-derived calli. Early changes in putrescine levels were detected in both cultures before the visible emergence of roots or somatic embryos. DFMO rapidly inhibited putrescine accumulation and growth in non-embryogenic calli and highly stimulated rooting activity. DFMO partially inhibited putrescine accumulation in embryogenic calli. This inhibition had no effects on callus growth but significantly reduced the time of emergence of roots and highly stimulated somatic embryo production. The relationship among putrescine, putrescine metabolism, growth, root and somatic embryo formation is discussed. 相似文献
159.
再生植株具有高频率的染色体异常,其中有20.61%表现为染色体数量变异,最常见的为2n—1类型,其次为2n—2类型,也有2n 1、2n—3个体以及染色体数嵌合株。再生植株减数分裂各期均有染色体异常行为,可以见到的有落后染色体、染色体桥、断片、二分体延迟、微核,还有粗线期十字型配对等结构变异,以及五分体、六分体和畸型四分体等异常现象。微核率随培养时间延长而增加,可用作染色体伤害的一个指标。再生植株R_1代存在着许多形态学变异。性状变异与染色体数目变异没有明显关系。 相似文献
160.
中国两种掌突蟾(锄足蟾科Pelobatidae,无尾目Anura)的细胞遗传学研究 总被引:1,自引:0,他引:1
本文对分布于云南境内的两种Leptolalax——L.ventripunctatus和L.alpinus的常规Giemsa核型、C-带和Ag-NORs作了研究,结果表明L.ventripunctatus的2n=22,20M 2T,NF=42,1对Ag-NORs位于5(?),并呈现异形现象,该区域亦显C-带正染;L.alpinus 2n=24,14M 4SM 6T,NF=42,1对Ag-NORs位于No.8短臂端部,并有随体联合现象。两种的着丝点区域均呈现C-带正染。 相似文献