全文获取类型
收费全文 | 35152篇 |
免费 | 4328篇 |
国内免费 | 2682篇 |
专业分类
电工技术 | 7390篇 |
技术理论 | 3篇 |
综合类 | 3888篇 |
化学工业 | 2732篇 |
金属工艺 | 549篇 |
机械仪表 | 2318篇 |
建筑科学 | 2109篇 |
矿业工程 | 891篇 |
能源动力 | 1688篇 |
轻工业 | 1398篇 |
水利工程 | 2138篇 |
石油天然气 | 1452篇 |
武器工业 | 479篇 |
无线电 | 2975篇 |
一般工业技术 | 1948篇 |
冶金工业 | 1402篇 |
原子能技术 | 254篇 |
自动化技术 | 8548篇 |
出版年
2024年 | 65篇 |
2023年 | 379篇 |
2022年 | 815篇 |
2021年 | 1086篇 |
2020年 | 1080篇 |
2019年 | 872篇 |
2018年 | 807篇 |
2017年 | 948篇 |
2016年 | 1237篇 |
2015年 | 1371篇 |
2014年 | 2257篇 |
2013年 | 2143篇 |
2012年 | 2844篇 |
2011年 | 2894篇 |
2010年 | 2347篇 |
2009年 | 2381篇 |
2008年 | 2386篇 |
2007年 | 2814篇 |
2006年 | 2571篇 |
2005年 | 2135篇 |
2004年 | 1789篇 |
2003年 | 1455篇 |
2002年 | 1248篇 |
2001年 | 989篇 |
2000年 | 868篇 |
1999年 | 579篇 |
1998年 | 405篇 |
1997年 | 308篇 |
1996年 | 261篇 |
1995年 | 211篇 |
1994年 | 145篇 |
1993年 | 85篇 |
1992年 | 74篇 |
1991年 | 74篇 |
1990年 | 55篇 |
1989年 | 41篇 |
1988年 | 41篇 |
1987年 | 24篇 |
1986年 | 12篇 |
1985年 | 12篇 |
1983年 | 5篇 |
1982年 | 4篇 |
1981年 | 5篇 |
1980年 | 3篇 |
1978年 | 3篇 |
1959年 | 6篇 |
1957年 | 2篇 |
1956年 | 2篇 |
1954年 | 2篇 |
1951年 | 2篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
101.
S. Meier L.R. McNaughton R. Handcock P.R. Amer P.R. Beatson J.R. Bryant K.G. Dodds R. Spelman J.R. Roche C.R. Burke 《Journal of dairy science》2021,104(3):3707-3721
This study investigated the hypothesis that dairy heifers divergent in genetic merit for fertility traits differ in the age of puberty and reproductive performance. New Zealand's fertility breeding value (FertBV) is the proportion of a sire's daughters expected to calve in the first 42 d of the seasonal calving period. We used the New Zealand national dairy database to identify and select Holstein-Friesian dams with either positive (POS, +5 FertBV, n = 1,334) or negative FertBV (NEG, ?5% FertBV, n = 1,662) for insemination with semen from POS or NEG FertBV sires, respectively. The resulting POS and NEG heifers were predicted to have a difference in average FertBV of 10 percentage points. We enrolled 640 heifer calves (POS, n = 324; NEG, n = 316) at 9 d ± 5.4 d (± standard deviation; SD) for the POS calves and 8 d ± 4.4 d old for the NEG calves. Of these, 275 POS and 248 NEG heifers were DNA parent verified and retained for further study. The average FertBV was +5.0% (SD = 0.74) and ?5.1% (SD = 1.36) for POS and NEG groups, respectively. Heifers were reared at 2 successive facilities as follows: (1) calf rearing (enrollment to ~13 wk of age) and (2) grazier, after 13 wk until 22 mo of age. All heifers wore a collar with an activity sensor to monitor estrus events starting at 8 mo of age, and we collected weekly blood samples when individual heifers reached 190 kg of body weight (BW) to measure plasma progesterone concentrations. Puberty was characterized by plasma progesterone concentrations >1 ng/mL in at least 2 of 3 successive weeks. Date of puberty was defined when the first of these samples was >1 ng/mL. Heifers were seasonally bred for 98 d starting at ~14 mo of age. Transrectal ultrasound was used to confirm pregnancy and combined with activity data to estimate breeding and pregnancy dates. We measured BW every 2 wk, and body condition and stature at 6, 9, 12, and 15 mo of age. The significant FertBV by day interaction for BW was such that the NEG heifers had increasingly greater BW with age. This difference was mirrored with the significant FertBV by month interaction for average daily gain, with the NEG heifers having a greater average daily gain between 9 and 18 mo of age. There was no difference in heifer stature between the POS and NEG heifers. The POS heifers were younger and lighter at puberty, and were at a lesser mature BW, compared with the NEG heifers. As a result, 94 ± 1.6% of the POS and 82 ± 3.2% of the NEG heifers had reached puberty at the start of breeding. The POS heifers were 20% and 11% more likely to be pregnant after 21 d and 42 d of breeding than NEG heifers (relative risk = 1.20, 95% confidence interval of 1.03–1.34; relative risk = 1.11, 95% confidence interval of 1.01–1.16). Results from this experiment support an association between extremes in genetic merit for fertility base on cow traits and heifer reproduction. Our results indicate that heifer puberty and pregnancy rates are affected by genetic merit for fertility traits, and these may be useful phenotypes for genetic selection. 相似文献
102.
G.A. Oliveira Junior F.S. Schenkel L. Alcantara K. Houlahan C. Lynch C.F. Baes 《Journal of dairy science》2021,104(8):9002-9015
Genetic improvement is a crucial tool to deal with the increasing demand for high quality, sustainably produced dairy. Breeding programs are based on genetic parameters, such as heritability and genetic correlations, for economically important traits in a population. In this study, we estimated population genetic parameters and genetic trends for 67 traits evaluated on heifers and first-lactation Canadian Holstein cows. The data consisted of approximately 500,000 records with pedigree information collected from 1980 to 2019. Genetic parameters were estimated using bivariate linear animal models under a Bayesian approach. Analyses for the 67 traits resulted in 2,211 bivariate combinations, from which the estimated genetic parameters are reported here. The most highly heritable traits were fat percent (0.66) and protein percent (0.69), followed by stature (0.47). Lowest heritabilities (0.01) were observed for disease-related traits, such as lameness and toe ulcer, and calf survival. The genetic correlations between gestation length, calf size, and calving ease measured on both heifer and cows were close to unity. On the other hand, traits such as body condition score and pin width, cystic ovaries and sole ulcer, rear teat placement, and toe ulcer were genetically unrelated. This study reports genetic parameters that have not been previously published for Canadian Holstein cows, and provides updates of those previously estimated. These estimates are useful for building new indexes, updating existing selection indexes, and for predicting correlated responses due to inclusion of novel traits in the breeding programs. 相似文献
103.
Alejandro Saborío-Montero Adrían López-García Mónica Gutiérrez-Rivas Raquel Atxaerandio Idoia Goiri Aser García-Rodriguez José A. Jiménez-Montero Carmen González Javier Tamames Fernando Puente-Sánchez Luis Varona Magdalena Serrano Cristina Ovilo Oscar González-Recio 《Journal of dairy science》2021,104(7):8135-8151
The rumen is a complex microbial system of substantial importance in terms of greenhouse gas emissions and feed efficiency. This study proposes combining metagenomic and host genomic data for selective breeding of the cow hologenome toward reduced methane emissions. We analyzed nanopore long reads from the rumen metagenome of 437 Holstein cows from 14 commercial herds in 4 northern regions in Spain. After filtering, data were treated as compositional. The large complexity of the rumen microbiota was aggregated, through principal component analysis (PCA), into few principal components (PC) that were used as proxies of the core metagenome. The PCA allowed us to condense the huge and fuzzy taxonomical and functional information from the metagenome into a few PC. Bivariate animal models were applied using these PC and methane production as phenotypes. The variability condensed in these PC is controlled by the cow genome, with heritability estimates for the first PC of ~0.30 at all taxonomic levels, with a large probability (>83%) of the posterior distribution being >0.20 and with the 95% highest posterior density interval (95%HPD) not containing zero. Most genetic correlation estimates between PC1 and methane were large (≥0.70), with most of the posterior distribution (>82%) being >0.50 and with its 95%HPD not containing zero. Enteric methane production was positively associated with relative abundance of eukaryotes (protozoa and fungi) through the first component of the PCA at phylum, class, order, family, and genus. Nanopore long reads allowed the characterization of the core rumen metagenome using whole-metagenome sequencing, and the purposed aggregated variables could be used in animal breeding programs to reduce methane emissions in future generations. 相似文献
104.
Ji-Su Kwon Jae-Young Nam Seon-In Yeom Won-Hee Kang 《International journal of molecular sciences》2021,22(5)
Bacterial wilt (BW) disease from Ralstonia solanacearum is a serious disease and causes severe yield losses in chili peppers worldwide. Resistant cultivar breeding is the most effective in controlling BW. Thus, a simple and reliable evaluation method is required to assess disease severity and to investigate the inheritance of resistance for further breeding programs. Here, we developed a reliable leaf-to-whole plant spread bioassay for evaluating BW disease and then, using this, determined the inheritance of resistance to R. solanacearum in peppers. Capsicum annuum ‘MC4′ displayed a completely resistant response with fewer disease symptoms, a low level of bacterial cell growth, and significant up-regulations of defense genes in infected leaves compared to those in susceptible ‘Subicho’. We also observed the spreading of wilt symptoms from the leaves to the whole susceptible plant, which denotes the normal BW wilt symptoms, similar to the drenching method. Through this, we optimized the evaluation method of the resistance to BW. Additionally, we performed genetic analysis for resistance inheritance. The parents, F1 and 90 F2 progenies, were evaluated, and the two major complementary genes involved in the BW resistance trait were confirmed. These could provide an accurate evaluation to improve resistant pepper breeding efficiency against BW. 相似文献
105.
106.
Maria Tziastoudi Georgios Pissas Georgios Raptis Christos Cholevas Theodoros Eleftheriadis Evangelia Dounousi Ioannis Stefanidis Theoharis C. Theoharides 《International journal of molecular sciences》2021,22(9)
Chronic kidney disease (CKD) is an important global public health problem due to its high prevalence and morbidity. Although the treatment of nephrology patients has changed considerably, ineffectiveness and side effects of medications represent a major issue. In an effort to elucidate the contribution of genetic variants located in several genes in the response to treatment of patients with CKD, we performed a systematic review and meta-analysis of all available pharmacogenetics studies. The association between genotype distribution and response to medication was examined using the dominant, recessive, and additive inheritance models. Subgroup analysis based on ethnicity was also performed. In total, 29 studies were included in the meta-analysis, which examined the association of 11 genes (16 polymorphisms) with the response to treatment regarding CKD. Among the 29 studies, 18 studies included patients with renal transplantation, 8 involved patients with nephrotic syndrome, and 3 studies included patients with lupus nephritis. The present meta-analysis provides strong evidence for the contribution of variants harbored in the ABCB1, IL-10, ITPA, MIF, and TNF genes that creates some genetic predisposition that reduces effectiveness or is associated with adverse events of medications used in CKD. 相似文献
107.
目的 提高脂溶性番茄红素的生物利用率和稳定性。方法 采用熔融-高速剪切法制备番茄红素纳米结构脂质载体。以包封率、平均粒径为主要评价指标,进行单因素实验,并在单因素基础上通过遗传算法结合Box-Behnken响应面法对制备工艺进行优化。结果 遗传算法和Box-Behnken响应面法优化得到的理论包封率分别为86.208 2%、86.169 5%。通过验证实验得到实际包封率为(86.267±0.44)%,平均粒径为(121.8±5.20)nm。结论 结果表明遗传算法结合Box-Behnken响应面法优化番茄红素纳米结构脂质载体模型可靠。 相似文献
108.
109.
110.
文章简要介绍了福建省危险废物综合处置场安全填埋场的防渗系统设计,着重对安全填埋场运行过程中如何防止渗滤液导排堵塞、主防渗膜被破损进行分析,提出解决方案或建议,并对固化体养护、清污分流、气体导排等一系列问题进行探讨。 相似文献