全文获取类型
收费全文 | 19813篇 |
免费 | 1016篇 |
国内免费 | 31篇 |
出版年
2023年 | 168篇 |
2022年 | 227篇 |
2021年 | 741篇 |
2020年 | 435篇 |
2019年 | 466篇 |
2018年 | 691篇 |
2017年 | 631篇 |
2016年 | 836篇 |
2015年 | 959篇 |
2014年 | 1201篇 |
2013年 | 1661篇 |
2012年 | 1747篇 |
2011年 | 1529篇 |
2010年 | 912篇 |
2009年 | 779篇 |
2008年 | 922篇 |
2007年 | 877篇 |
2006年 | 768篇 |
2005年 | 679篇 |
2004年 | 552篇 |
2003年 | 456篇 |
2002年 | 405篇 |
2001年 | 335篇 |
2000年 | 305篇 |
1999年 | 272篇 |
1998年 | 115篇 |
1997年 | 81篇 |
1996年 | 100篇 |
1995年 | 83篇 |
1994年 | 66篇 |
1993年 | 66篇 |
1992年 | 179篇 |
1991年 | 165篇 |
1990年 | 134篇 |
1989年 | 102篇 |
1988年 | 145篇 |
1987年 | 111篇 |
1986年 | 93篇 |
1985年 | 92篇 |
1984年 | 92篇 |
1983年 | 51篇 |
1982年 | 45篇 |
1981年 | 52篇 |
1980年 | 47篇 |
1979年 | 66篇 |
1978年 | 38篇 |
1977年 | 45篇 |
1976年 | 37篇 |
1974年 | 34篇 |
1973年 | 32篇 |
排序方式: 共有10000条查询结果,搜索用时 28 毫秒
11.
12.
Phytochemical analysis of dried twigs of Marsdenia roylei (family Asclepiadaceae) has resulted in the isolation of a trisaccharide, maryal, and a diglycoside, rolinose. Their structures were determined as O-beta-D-oleandropyranosyl-(1-->4)-O-beta-D-digitoxopyranosyl++ +-(1-->4)-D- cymaral and ethyl O-beta-D-oleandropyranosyl-(1-->4)-O-3-O-methyl-6-deoxy-beta-D- allopyranoside, respectively, by chemical degradation and spectroscopic methods. 相似文献
13.
14.
Vinod Kumar 《Chronobiology international》1986,3(3):165-170
Groups of photosensitive, unstimulated or stimulated, male blackheaded buntings were subjected to photoregimes of 15 hr of green light of three intensities and 9 hr of dark per day. In some groups green light was interrupted with 90 min of bright fluorescent light at different times in the subjective day. While gonads did not develop or regressed in some groups, birds in others behaved as if exposed to long daylengths. The results besides suggesting the involvement of endogenous circadian rhythm during initiation and maintenance of gonadal growth indicate that the reproductive rhythms are entrained and induced by environmental photoperiod. 相似文献
15.
This study was conducted to study the long-term impact of bioinoculants, Azotobacter chroococcum and arbuscular mycorrhizal fungi (AMF) on growth and biomass yield of Jatropha curcas grown in nursery and in field conditions. The experiment was set up in a randomized block design, and the following treatments was designed (T1 = control, T2 = Azotobacter, T3 = inoculation with AMF, and T4 = inoculation with Azotobacter + AMF). Data on various growth attributes (shoot height and shoot diameter) and biochemical parameters [leaf relative water content (LRWC), sugars, protein, and photosynthetic pigments] were recorded up to 6 months in the nursery and in the field (18 months). Results pertaining to morpho-physiological traits showed Azotobacter and AMF consortia increase shoot height, shoot diameter, LRWC, sugars, proteins, and photosynthetic pigments over control under nursery conditions. Besides enhancing the plant growth, these bioinoculants helped in better establishment of Jatropha plants under field conditions. A significant improvement in the shoot height, shoot diameter, fruit yield/plant, and seed yield (g)/plant was evident in 18-month-old Jatropha plants under field conditions when Azotobacter and AMF were co-inoculated. This work supports the application of bioinoculants for establishment of Jatropha curcas in semi-arid regions. 相似文献
16.
17.
18.
Ratul Saha Robert S. Donofrio Susan T. Bagley 《Journal of industrial microbiology & biotechnology》2010,37(8):843-848
A TaqMan quantitative real-time polymerase chain reaction (qPCR) assay was developed for the detection and enumeration of
three Pseudomonas species belonging to the mendocina sublineage (P. oleovorans, P. pseudoalcaligenes, and P. oleovorans subsp. lubricantis) found in contaminated metalworking fluids (MWFs). These microbes are the primary colonizers and serve as indicator organisms
of biodegradation of used MWFs. Molecular techniques such as qPCR are preferred for the detection of these microbes since
they grow poorly on typical growth media such as R2A agar and Pseudomonas isolation agar (PIA). Traditional culturing techniques not only underestimate the actual distribution of these bacteria but
are also time-consuming. The primer–probe pair developed from gyrase B (gyrB) sequences of the targeted bacteria was highly sensitive and specific for the three species. qPCR was performed with both
whole cell and genomic DNA to confirm the specificity and sensitivity of the assay. The sensitivity of the assay was 101 colony forming units (CFU)/ml for whole cell and 13.7 fg with genomic DNA. The primer–probe pair was successful in determining
concentrations from used MWF samples, indicating levels between 2.9 × 103 and 3.9 × 106 CFU/ml. In contrast, the total count of Pseudomonas sp. recovered on PIA was in the range of <1.0 × 101 to 1.4 × 105 CFU/ml for the same samples. Based on these results from the qPCR assay, the designed TaqMan primer–probe pair can be efficiently
used for rapid (within 2 h) determination of the distribution of these species of Pseudomonas in contaminated MWFs. 相似文献
19.
Uranium (U) tolerant aerobic heterotrophs were isolated from the subsurface soils of one of the pre-mined U-rich deposits at Domiasiat located in the north-eastern part of India. On screening of genomic DNA from 62 isolates exhibiting superior U and heavy metal tolerance, 32 isolates were found to be positive for PIB-type ATPase genes. Phylogenetic incongruence and anomalous DNA base compositions revealed the acquisition of PIB-type ATPase genes by six isolates through horizontal gene transfer (HGT). Three of these instances of HGT appeared to have occurred at inter-phylum level and the other three instances indicated to have taken place at intra-phylum level. This study provides an insight into one of the possible survival strategies that bacteria might employ to adapt to environments rich in uranium and heavy metals. 相似文献
20.